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What is a Modular Process Skid? Advantages, Applications, and Characteristics of a Modular Skid Design

Written by Anup Kumar Dey in Process

A modular skid or modular process skid is a self-contained process system contained within a frame or module including equipment, piping, and instrumentation. This is basically a machine-in-a-box design. To reduce delays resulting from long lead times of equipment, on-site fabrication process, and to-and-fro communication between vendors, many organizations prefer the modular skid design that reduces project time and increases profit.

Modular process skids are one of the best alternatives to traditional stick-built construction. In the traditional approach, individual process system parts are shipped separately and then assembled at the construction site. This not only increases the production/fabrication time but also creates a hazardous environment. By accepting the piping, instrumentation, and equipment in a modular skid form companies reduce the project time as well as cost.

In recent times, modular process skids have been widely used in chemical, pharmaceutical, consumer products, manufacturing, oil and gas, power, food and beverage, and petrochemical industries. They are easy to transport and integrate with the system. Fig. 1 below shows a typical modular process skid.

Typical Modular Process Skid
Fig 1: Example of a Typical Modular Process Skid

Advantages of Modular Process Skids

The main advantages that prove the growing popularity of modular skid systems are:

  • Reduces time and labor cost
  • No geographic limitation
  • Less space requirement
  • Portability.
  • High-quality fabrication within a controlled environment and manufacturer facilities.
  • The standardized design of modular skids reduces engineering design costs as well.
  • Parallel civil site up-gradation working at the site while the skid is being produced at manufacturer facilities.
  • Testing at manufacturer facility.
  • Easier inspection and proper documentation.
  • Minimal site work.
  • Increased reliability
  • Reduced safety concerns and improved security.

Features of modular skid design and layout

Modular process skids are developed to contain a complete process system. They make a complete unit of operations and organize a manufacturing process into logical units. All such process skids usually have the following characteristic features:

Portable Robust Design: Modular skid systems must be designed to provide robust design built within frames. They shall be easy to transport.

Small Footprint: The design of modular process skids is compact. They fit into a smaller footprint combining the piping, tanks, instrumentation, and necessary process equipment.

Easier Process Connection: By gathering all process connections into one spot on the skid, the modular skid design makes plant connections easier.

Controlled assembly: As the modular process skids are manufactured in controlled conditions offsite, the existing operations remain unaffected by skid fabrication.

FAT testing before installation: Before modular process skids are shipped to the site, the required factory acceptance testing (FAT) is completed which in turn reduces on-site startup time.

Accessible layout: All modular process skids are designed considering accessibility and major pieces of equipment placed around the edge of the frame.

Components of Modular Process Skids

Modular process skids usually consist of the following elements:

Applications of Modular Skid Systems

Modular process skid systems are used in a range of applications. Some of the typical uses of modular skids are:

  • Chemical processing
  • Batch processing
  • Wellhead control panel
  • Biowaste deactivation systems
  • Centrifuge systems
  • Distillation
  • Clean-in-place systems
  • Coating systems
  • Lubrication Systems
  • Wastewater treatment systems
  • Continuous production systems
  • Demonstration plants
  • Pilot plants
  • Furnaces or Fired Heaters
  • Flavor mixing and blending
  • Food and beverage processing
  • Refining
  • Fuel delivery systems
  • In-line blending systems
  • Mixing systems
  • Metering system
  • Perfume mixing
  • Petroleum processing
  • Raw materials processing
  • Processing plants
  • Pump carts
  • Fluid process
  • Filtration system
  • Separation unit
  • Dosing unit
  • Fire and gas detection system

Selecting a Modular Skid

Modular process skids make a significant difference in the company’s project cycle. So, whenever it is feasible, a modular skid design shall be selected. However, the modular process skid design may not be feasible in all situations. For example, when the individual process elements are large and can not fit within the frame of the skid, traditional construction methods need to be followed.

Sometimes multiple individual modular skids are combined together to form a larger process system.

Modular Skid Suppliers

Several companies provide modular process skids such as,

  • Integrated Flow Solutions LLC
  • ANDERSON DAHLEN
  • Thomas
  • EKME
  • Gulf Specialized Work (GSW)

Disadvantages of Modular Process Skid

Modular Skid-mounted process units in a refinery are normally limited to small plants because
larger & heavier units are not suitable for constructing as well as shipping to the manufacturing site as it costs high.

Process modular skids tend to be cramped with tight spacing between equipment. The low
space between the equipment makes it troublesome to the operators, particularly during
maintenance activity.

What is a Link Seal? Its Advantages, Applications, Sizing, Working, and Installation

Written by Anup Kumar Dey in Civil,Construction,Maintenance,Piping Design Basics

Link-Seals are mechanical seals for creating air, water, or a gas-tight seal between a pipe and a core hole. They are available in a belt form with a series of interconnecting rubber links, pressure plates, and bolts. For sealing a pipe or cable with a casing sleeve/ pipe sleeve, duct, or wall, link-seal systems are proven to be very useful and hence find wide applications in various industries. They are believed to be one of the premier methods for permanent sealing of the annular space between the pipes & any size of walls, floors, or ceiling penetrations. In actual practice, link seals can be used to quickly, easily, and permanently seal any kind of cylindrical object with its penetration barriers. In the oil and gas industries, Link-Seal Modular Seal designs have the capability to seal pipe penetrations ranging in size from 10 mm to 3.6m in diameter.

Advantages of Link Seal Systems

Link seal systems as a permanent sealing system provide several benefits as mentioned below:

  • Positive hydrostatic sealing.
  • Resistant to temperature (-500C to 2040C), and chemical attack (corrosion).
  • Long sealing life.
  • Easy to adjust and re-fit.
  • Possible to install during the pipe operation, no plant shutdown is required.
  • Available in fire-rated form.
  • Can absorb slight pipe movements.
  • Economical.
  • Once installed, almost maintenance-free.
  • Link seals are available in various sizes to suit any requirement.
  • Absorbs shock, sound, and vibration

Applications of Link-Seal

Because of the above-mentioned advantages, Link seal systems are widely in almost all types of industries. Some of the applications of link seals are mentioned below:

  • Manhole Pipe Entry Seals
  • Cased Road Crossings
  • Thermal Storage Systems
  • Dual Containment Seals
  • Fire Protection Wall Penetrations
  • Waste Treatment Plants
  • Cased Railroad Crossings
  • Electrical Isolation of Pipes
  • Precast Concrete Vault Seals
  • Insulated Pipe Seals
  • Noise Dampening
  • Flexible Sign & Pole Supports
  • Marine Applications
  • Electrical Isolation of Pipe Supports
  • Mining Industries
  • Pulp & Paper Industries
  • Decorative Fountains
  • High-Pressure Tank Guards
  • Underground Steel Tanks
  • Electrical Contractors
  • Valve and Flange Pits
  • Pool Contractors
  • Waste Water Treatment
  • Telecommunications
  • Refrigeration Buildings
  • Guard Post Assemblies
  • Power Generation Dams
  • Offshore Oil Rigs
  • Coal Preparation Plants
  • Tunneling Operations
  • Precast Concrete Manufacturers
  • Perimeter Berm Installations Around Tank Farms
  • Flow Restrictors in Sewer Maintenance
  • Fluid Overflow Devices
  • Noise and Sway Dampener
  • Through Deck Fire Breaks
  • Bridge Construction
  • Septic Tank Installations

How Does a Link Seal Work?

While installing the link-seal belt is positioned between the pipe and the annular wall. Then following the proper tightening sequence the link-seal is tightened. Once installed the link-seals provide a pressure-tight and secure sealing by the radial expansion of the rubbers in the annual spaces. Refer to the following image that shows the sectional drawing of a wall penetration sealed with a link seal.

Sectional drawing of Link-Seal working
Fig. 1: Sectional drawing of Link-Seal working

Installation of Link-Seal System

The installation sequence of a link-seal system (Fig. 2) is provided below:

  1. Centre the pipe in the casing or wall opening. The pipe should be supported adequately on both ends.
  2. Loosen the rear pressure plate of the link-seal belt with a nut such that the links can move freely. Connect both ends of the belt around the pipe.
  3. Ensure that all bolt heads of the link-seal system are facing the installer. Extra slack or sag is normal. Hence, Do not remove links if extra slack exists.
  4. Slide the belt assembly into the annular space.
  5. Using a hand socket Allen head, hand socket, or off-set wrench, start at 12 o’clock. Do not tighten any bolt more than 4 turns at a time. Continue in a clockwise manner until links have been uniformly compressed.
  6. Make 2 or 3 more passes at 4 turns per bolt, tightening all bolts clockwise until all sealing elements “bulge” around all pressure plates
  7. Once all sealing elements bulge out, the link seal installation is complete and ready for use.
Link Seal Installation Sequence
Fig. 2: Link Seal Installation Sequence

Sizing of Link Seal

Proper sizing of link seals is very important. It requires calculating some parameters. The link seal sizing sequence is provided below:

Calculating Annular Space: The annular space is half the difference between the actual pipe O.D. and the actual wall I.D. opening diameter. The following equation can be used:

Annular Space=(ID of wall opening or sleeve-Actual Pipe OD)/2

Calculating the number of links required: To find the number of links first we have to calculate the bolt circle diameter using the following formula:

Bolt Circle Diameter=(Wall/Sleeve opening ID+Pipe Actual OD)/2

Next, the number of links for each seal can be calculated as follows:

Number of links per seal=(Bolt circle diameter X 3.14)/Arc Length

Arc length or Chord length will be available in the manufacturer catalogs.

Once the above parameters are calculated, the required link-seal can easily be selected from the manufacturer’s catalog.

Link Seal Sizing Chart

A typical link seal size chart is provided in Fig. 3 below as a sample. The manufacturer catalog must be followed during actual link-seal sizing and selection.

Link-Seal Sizing Chart
Fig. 3: Typical Link-Seal Sizing Chart

Link Seal Catalog

Some of the link-seal manufacturer catalogs are provided below for more learning and reference.

What is Valve Coefficient (Cv) or Flow Coefficient? | Importance of Valve Cv

Written by Anup Kumar Dey in Process

What is the Valve Coefficient?

The Valve Coefficient or Flow Coefficient of a valve is a convenient method to relate flow rates to the pressure drop. It provides a relative measure of the efficiency of a valve. The valve coefficient is usually denoted by Cv.

In a general sense, the valve flow coefficient, or Cv is a number that represents a valve’s ability to pass the flow through it. The bigger the value of Cv, the more will be the flow through the valve with a given pressure drop. Also, the valve Cv is directly related to the valve opening. The larger the valve opening, the larger is the Cv. The highest possible Valve Coefficient for a valve is found when the valve is fully open.

What is the unit of Cv?

The unit of Valve coefficient Cv is US gal/min, lbf/in2. However, there are some other notations like Kv or f depending on units. Kv is measured in units of l/min, bar, and f is measured in units of Imp gal/min, lbf/in2. Note that, all three can easily be converted to one another using the factors given in Table 1.

 KvCvf
Kv–14.2817.09
Cv0.07–1.1966
f0.05890.8357–
Table 1: Cv, Kv, and f conversion factors

How do you find the Coefficient of a Valve?

The equations for valve coefficient are different for liquids and gases. The mathematical equation of the Valve coefficient is given below.

Valve Coefficient Cv for Liquids

The Valve coefficient for liquids are given by

Cv=Q*√(SG/ΔP)

Here,

  • Q denotes the rate of flow (US gallons per minute).
  • SG denotes the specific gravity of the fluid (for water = 1).
  • ΔP is the pressure drop across the valve (in psi).
  • Cv is the valve flow coefficient.

So following the above equation the Valve coefficient, Cv for liquids can be defined as the volume of water at 60°F that will flow per minute through a valve with a pressure drop of 1 psi across the valve.

A Cv value of a valve is 1 means a valve will pass 1 gallon per minute (GPM) of 60oF water with a pressure drop (Dp) of 1 (PSI) across the valve. Similarly, a valve with a Cv of 280 will pass 280 GPM of 60oF water with a pressure drop of 1 PSI.

Valve Co-efficient Cv for Gases

For gases (non-critical flow) the valve coefficient is given by

Cv=0.06223Q√[(T*SG)/{Z*(P12-P22)}

Here,

  • Q is the rate of flow (Standard cubic feet per minute).
  • P1 is the upstream Pressure (in psia)
  • P2 is the downstream Pressure (in psia)
  • Z is the compressibility factor
  • T is the absolute temperature (in 0K)
  • SG is the specific gravity (for air =1)

For the critical flow of gases, Cv is determined using the following formula:

Cv=0.06223(Q/P1J)√{(T*SG)/Z}

Here, J is a function of specific heat ratio (r) and (R=P2/P1) which can be taken from Table 2

Sr NorRJ Sr NorRJ
11.20.5640.825 91.360.5350.845
21.220.5610.828 101.380.5320.847
31.240.5570.832 111.40.5280.849
41.260.5530.833 121.420.5240.851
51.280.5490.836 131.440.5210.853
61.30.5460.838 141.460.5180.855
71.320.5420.84 151.480.5150.857
81.340.5390.843 161.50.5120.859
Table 2: Values of J for finding Cv of Gases in critical flow

The valve coefficient is very important in valve selection as it helps in deciding the proper valve size for a particular application. The valve size, degree of valve opening, detail design, and construction of the valve affect the valve coefficient. Usually, the valve coefficient is quoted for individual valves with a full opening.

What is the Significance of Valve Coefficient (Cv)?

Improper Cv for a valve may diminish its performance in any one of the following ways:

When the calculated Cv is small as compared to the Cv required for a specific application:

  • The valve or the inside trim will be undersized, which will create starvation for the process fluid.
  • Restriction in the valve can increase the upstream pressure which may cause the failure of upstream equipment.
  • There could be a higher pressure drop than expected leading to cavitation or flashing.

On the other hand, if the estimated Cv is high for a required process,

  • Higher Cv will lead to the selection of larger, oversized valves which in turn will increase the cost, space requirement, and weight.
  • Higher Cv will create a significant control problem if the valve is used in the throttling service. Also, there will be higher pressure drops and faster velocities leading to cavitation, flashing, or erosion of the trim parts.

Why should I care about Valve Coefficients?

Having a preliminary understanding of Cv can help in several ways:

  • The knowledge of Cv will help in the right size valve selection for a specific application.
  • It is possible to compare valves from different companies and their flow capacities.
  • The value of Cv will give an understanding of the effect of pressure on the system.

Each valve has its valve coefficient. According to the piping configuration or trim design, valve manufacturers usually publish these Cv data for various valve styles. Sometimes they provide a Cv curve that provides the relationship of valve flow coefficient concerning valve opening.

How to Combine Valve Flow Coefficients?

Valve flow coefficients can easily be combined depending on the flow types in parallel or series.

  • For flow in parallel, the flow coefficients are combined as Cv=Cv1+Cv2+Cv2+Cv4+…
  • For flow in series, the flow coefficients are combined as follows: (1/Cv)2=(1/Cv1)2+(1/Cv2)2+(1/Cv3)2+(1/Cv4)2+….

What is a Cryogenic Valve in Piping? Its Features and Applications

Written by Anup Kumar Dey in Piping Design Basics

What is a Cryogenic Valve?

Piping and Pipeline systems handling liquid hydrogen, oxygen, helium, nitrogen, liquefied natural gas, or similar very cold fluids require to use of cryogenic valves. The term cryogenics deals with materials and processes below -1010C (-2390F). Hence, Cryogenic valves must be designed with properties to handle such low temperatures. The main difference between cryogenic valves from standard valves is that they are able to work in such low temperatures with high pressures.

Problems with Cryogenic Valves

The main problem with cryogenic valves is that any fluid leakage to the atmosphere through gaskets or gland seals will degrade the valve and associated equipment performance. Also, such leakage at the valve stem will cause localized icing that may seize the valve-operating mechanism. This is the reason valves for cryogenic applications must be designed for high performance and truly zero leakage as per API 598.

Codes and Standards for Cryogenic valves

Codes and standards used for cryogenic valves are:

  • BS 6364
  • BS EN 12567
  • BS EN 1626
  • BS EN 12300
  • MSS SP-134
  • ISO 28921-1
  • ISO 21011
  • ISO 10497
  • ASME B16.34

Why do cryogenic valves have long stems? | Design Consideration of Cryogenic Valves

All cryogenic valves for liquid natural gas, methane, oxygen, ammonia, etc applications are specially designed. Cryogenic valves usually have extended bonnets so that the valve stem seals are kept away from the cold source. This will serve two important purposes:

  • The valve stem seals will have a relatively higher temperature.
  • There will be sufficient space to provide insulation between the pipeline and the lever/handwheel operating the valve.

Size and Pressure Rating of Cryogenic Valves

Cryogenic valves for industrial applications can be found in various sizes and pressure classes. The size usually ranges from 1/8 inch to 88 inches (3 mm to 2240 mm). The pressure rating of cryogenic valves varies from ultra-high vacuum pressure to 700 bar. All these valves are capable of working at a temperature down to -2540 C (-4250F).

Materials for Cryogenic Valves

Usual materials that are used for constructing a cryogenic valve are Aluminum, Monel, Brass, Bronze, Stainless Steel, Incoly, Zirconium, etc. PTFE or graphite is normally used as the seal material.

Common Valves for Cryogenic Applications

Usual valves used for cryogenic applications are specially designed globe, angle, gate, butterfly, and ball valves. So, selecting the right type of cryogenic valve for the required application is essential. There are no strict available guidelines for valve type in cryogenic service. But, there is a trend to select quarter-turn ball valves and triple-offset butterfly valves.

Triple Offset Butterfly Valves for Cryogenic Services:

Triple-offset butterfly valves are high-performance widely used valves for cryogenic services. The offsets in such valves reduce the rubbing and wear between the seat and seal.

The triple offset design has a resilient stainless steel ring that is installed in the disk assembly to provide a zero-leakage seal for cryogenic duties.

The seal and seat contact surface is cone-in-cone construction. These cones are inclined and the contact angle between the seat and seal generates a slight wedging effect that flexes and radially compresses the disc-seal ring. Regardless of the flow direction or line pressure, the valve provides very good shut-off capability.

Cryogenic Valves
Typical Cryogenic Valves

Ball Valves for Cryogenic Application:

Piping and pipeline systems for LPG, LNG, thermal fluids, liquid oxygen, and nitrogen applications use double-seal ball valves. They can be of reduced and full bore types. Cryogenic ball valves incorporate a vapor space of sufficient height that allows gasification in the area below the gland. This keeps the gland packing at near ambient temperature.

With an increase in pipe sizes, the gate and globe valves become difficult and costly to actuate. That is the reason they are restricted to smaller pipe sizes and applications not requiring a remote operation.

Features of Cryogenic Valves

  • Cryogenic valves should be lightweight as the lightweight valve mass is easier to cool from ambient to cryogenic temperature.
  • Lighter cryogenic valves usually have lower conductivity that helps in reducing heat influx as compared to heavier constructions.
  • Flange and welded configurations are usually used for cryogenic piping connections. However, welded valves are better.
  • Cryogenic valves should be assembled in a clean room and be lubricant-free or utilize lubricants compatible with cold service. While purchasing a cryogenic valve, documented cleaning procedures must be collected to verify and follow proper procedures during the assembly process.

Testing of Cryogenic Valves

The following tests are usually required to perform for cryogenic valves:

  • Shell strength test: Hydrostatic or Pneumatic test to 1.5 × Maximum Working Pressure.
  • Shell leak test: For the leak test of the shell usually a Pneumatic test is performed with 1.1 × Maximum Working Pressure.
  • Seat leak test: Pneumatic test to 1.1 × Maximum Working Pressure.
  • Cryogenic prototype test: This test is performed following BS 6364 Appendix A.
  • Cryogenic production test: The procedures for Cryogenic testing of valves are provided in BS 6364 and the same is followed.

Where are Cryogenic Valves used? | Applications of Cryogenic Valves

Cryogenic valves are widely used in

  • LNG liquefaction plants
  • LNG terminals
  • LNG transportation systems
  • Food and beverage industries
  • Air separation plants
  • Steel production plants
  • Research laboratories
  • Chemical and petrochemical plants
  • Aerospace storage facilities

How Cryogenic Valve is installed in Piping?

To maintain a warm gas seal, the valve is located so that the stem has a minimum angle of 15 degrees to the horizontal. Preferably, the valve is in a horizontal pipe run to simplify piping arrangements.

What are Spool Valves? Their Types, Working, Construction, and Design Considerations

Written by Anup Kumar Dey in Piping Design Basics

A spool valve is part of a hydraulic system that controls/regulates the fluid flow of the system. The valve is made up of cylindrical spools that rotate or slide to allow or stop the flow. Spool valves are designed in such a way that the leakage in the spool is small compared to the hydraulic system flow rate. Spools are basically valve components with seals mounted along their surface. Upon activation of the spool shifts cause the seals to travel along the bore which opens the ports to allow flow.

To move the flow around a circuit of pipes, spool valves slide forward and backward. A spool valve consists of two basic components: a cylindrical barrel that slides a spool or plunger. Glands provide the blocking of the ports. It can also be done by the full-diameter spool section, with the intervening waist sections providing interconnection of the port through the barrel. These help in multi-way and multi-positioning switching.

Spool valves are simple and low-cost devices. A proper surface finish is required for the barrel bore and spool to get proper sealing. It also needs close tolerance to provide practical minimum clearance. Glandless spool valves usually require a lapped fit between the spool and the body.

Types of Spool Valves

Spool valves can be categorized into two types. They are:

  • Sliding spool valve and
  • Rotary spool valve

Sliding Spool Valve:

Sliding spool valves along with their lands and grooves are cylindrical in cross-section. They are the most popular and widely used spool valves in the industry. The spool in a spool valve is grooved and slides in and out of position within the sleeve. This action alternately blocks and opens the fluid intake and outtake portals. Sliding spool valves find applications in pneumatic and hydraulic fluid power systems to control the flow and its direction. There are various modes by which sliding spools can operate. Those are:

  • Manual operation,
  • Mechanical actuation,
  • Electrical means.
  • The pneumatic operation, or
  • Hydraulic or pilot control,

Rotary Spool Valves:

Rotary spool valves have spheres-like lands and grooves, in the form of holes. It consists of a fixed tubular sleeve, within which the core is rotating. Rotary spool valves work similarly to a revolving door, with each bend of the core functioning as a portal for hydraulic fluid to leave and enter the valve.

Extensively used in the machine tools industry, rotary spool valves got their name because of the rotational movement of the spool that opens or closed the fluid passage. They are usually manually operated and used in low-pressure applications with small flow rates.

Working of a Spool Valve

Spool valves are operated using either oil or air as the energy source. A spool valve has a cylinder inside a sealed outer case. Several chambers are drilled through the case from one side to the other to form ports. The spool moves within the sealed case. This movement ensures the opening and closing of these ports depending on the spool position. A spool valve can be operated using a button, lever, or by solenoid.

Spool valves are referred to using numbers such as 3/2, 4/2, 5/2, or 5/3, etc. Here, the first number indicates the number of ports and the second number informs the spool position. Spool valves are manufactured in a wide range of configurations.

Construction of Spool Valves

The cylindrical shaft known as the spool slides into a machined bore in the valve housing. The housing has inlet and outlet ports that connect the valve to the hydraulic system. The housing bore is divided by the lands of the spool into a series of separate chambers. The ports of the valve body lead into these chambers and the spool position determines the nature of interconnection between the ports.

Design Consideration of Spool Valves

As the spool valves work on a sliding principle, the design of these valves should follow the basics of sliding valves. Some of these design requirements to be controlled during the detail design stage of the spool valves are:

  • The ports should be pressure-balanced such that there is no net axial pressure force on the spool.
  • The diameter of the valve has suitable stiffness.
  • The valve body or sleeve must be adequately rigid.
  • To reduce friction forces, suitable material should be selected for sliding/rubbing parts.
  • To avoid unbalanced radial forces annular flow should be symmetrical.
  • Forces due to fluid momentum changes shall be minimized.

Configurations of Spool Valves

Mobile hydraulic systems widely use spool valves. The main reason is that in spool valves can easily adjust into two, three, or more positions to direct fluid between different combinations of inlet and outlet ports. With respect to their flow-directing states, there are four commonly applied neutral position configurations.

  • Open center
  • Closed-center
  • Tandem center
  • Float center

Advantages of a Spool Valve

Spool valves provide the following advantages:

  • As it has the ability to select from high, low, and vacuum pressures, Spool valves can be used as selector valves.
  • Spool Valves can be used to lock pressure downstream.
  • The pressure entering the valve from any given port does not affect the spool movement.
  • Less force is required to actuate as they are not affected by pressure.
  • The fluid entering the valve from any working port does not affect spool movement.

Disadvantages of Spool Valve

The main disadvantages of a spool valve are:

  • During actuation, all the ports are instantly opened to flow as the spool shifts.
  • Due to the smaller internal surface area, the flow rate is lower.
  • Product life is affected as the seals mounted on the pools are exposed to wear when traveling through the bore of the valve.
  • As the spool valves are usually designed with metal-to-metal sliding fits, some fluids may bypass these seals.

What is a Pinch Valve? Working, Types, Selection, and Advantages of a Pinch Valve

Written by Anup Kumar Dey in Piping Design Basics

A pinch valve is a flex-body valve with a flexible tube that can be pushed together or “pinched” mechanically through a mechanism or through fluid pressure to create a full closure of the flow path. The flow passage of these valves is straight without crevices and moving parts. The soft body of the pinch valves has the ability to seal around the trapped solids. This property makes pinch valves ideal for handling slurries, foodstuffs, and pharmaceuticals. Other industries where pinch valves find application are:

  • Cement industry
  • Plastic industry
  • Pneumatic Conveying industry
  • Wastewater industry/Sewage treatment plants
  • Ceramic Industry
  • Environmental Industry
  • Chemical industry
  • Mining industry
  • dosing and weighing systems
  • Commercial vehicle industry
  • Bulk and solid handling industry, etc.

Also known as clamp valves, pinch valves are designed to control or shut off the flow from abrasive, granular, fibrous, or corrosive media. The Pinch Valve finds its wide application as an isolating or regulating valve for sludges, dust, emulsions, gaseous materials, powder, compressed air, granulates, pellets, etc.

Working principle of a Pinch Valve

A pinch valve has three major parts: (i) a housing, (ii) an elastomeric rubber sleeve, and (iii) end connections. The elastomeric tube is fitted into the housing from the inlet to the outlet with a pinch bar mechanism and is the only component to be in contact with the flowing media. The end connections can be screwed, bolted, or threaded at each end to provide support and connection.

Pinch valve Working and Components
Fig. 1: Pinch valve Working and Components

The pinch mechanism can be of various types. A simple screw-operated mechanism with a pinch only on one side of the tube or a differential screw with two pinching mechanisms. Mechanical mechanisms using air or hydraulic pressure to squeeze the tube can also be used.

In normal conditions, the pinch valve is open. When air or hydraulic pressure is applied to the valve, it pushes down the elastomeric rubber sleeve, creating a pinching effect. When the sleeve is fully pinched, the flow is restricted, and the valve is closed. The rubber sleeve in a pinch valve has the capability to trap the particles around it, providing an excellent shut-off.

When the external pressure is released, the force of the flowing media and the rebounding property of the rubber completely open the valve. This fully opened valve provides free flow passage for the media that prevents the valve from blockage. As the media only comes in contact with the rubber tube, the media remains isolated which ensures no contamination.

Types of Pinch Valves

Depending on the body construction, pinch valves are of two types:

Open pinch valves: Usually mechanically pinched valves are of open type without metal body casing. For inspecting the valve body visually and physically during operation, the open construction of pinch valves is used. This is the most simple design but the liner is exposed to the environment.

Enclosed pinch valves: Enclosed-body pinch valves look similar to globe valves from outside. The housing is actually a protective casing for the liner. The pinching mechanism is housed inside the metallic casing.

Types of Pinch valves
Fig. 2: Types of Pinch valves

Depending on the pinching mechanism pinch valves can be of the following types:

  • Manual Pinch Valve
  • Air-Operated Pinch Valve and
  • Hydraulic pressure-operated pinch valve.

Pinch Valve Sleeves

The sleeves of pinch valves can be of various types including standard, double-wall for abrasive applications, cone sleeves for throttling purposes, and variable orifice sleeves for improved flow characteristics. Fig. 3 below shows these pinch valve sleeves.

Pinch Valve Sleeve Types
Fig. 3: Pinch Valve Sleeve Types

Selection of Pinch Valves

There are various important parameters that must be considered while selecting a pinch valve for a particular application. Some of these parameters are:

Pinch valve body material: Lightweight body material is preferred. The elastomeric sleeve should be carefully selected as it comes in direct contact with the flowing fluid. Usual rubber materials are EPDM, NBR, natural rubber, silicone, food quality rubber, GRS, Neoprene, Butyl, Buna-N, PTFE, FDA, Hypalon, etc. Good abrasion resistance to prevent damage is required.

Opening and Closing Pressure: For proper functioning of the pinch valve, the following pressure differentials must be considered:

  • Opening: The operating pressure should be more than the control pressure. The typical control pressure while the opening is 0 bar. Enough pressure differential is required so that the operating pressure is able to open the sleeve.
  • Closing: During the closing of the pinch valve, the control pressure has to be more than the operating pressure. In absence of enough pressure differential, the control pressure may not be able to overcome the operating pressure and close the valve by pushing the sleeve.

Design temperature: The valve material should be able to withstand the minimum and maximum temperatures that are expected for the application.

Size and Pressure Rating of Pinch Valves

Pinch valves can be used in a wide range of liquid and liquid-solid mixtures. However, the acceptable size of solids depends on the valve size and the precise design and construction of the tube. Pneumatic and hydraulic-powered versions are suitable for pressures up to 49 Barg. The common size and pressure rating of pinch valves are provided in the table below:

SizeMaximum Pressure, Barg
DN15 to DN2012
DN25 to DN15010
DN2008.5
DN250 to 3006.9
DN3505.1
DN400-DN6003.4
Size vs Pressure Rating of Common Pinch Valves

Advantages of Pinch Valve

With its unique design, a pinch valve provides various advantages like:

  • Suitable for use with abrasive and corrosive media
  • Low-weight, compact, simple, robust, & straight through design
  • Minimum turbulence and friction
  • Straight flow path without clogging by the media
  • No contamination
  • Quick opening and closing time
  • Low maintenance cost
  • Self-cleaning
  • Easy replacement of the rubber sleeves
  • Very good sealing properties
  • Low energy consumption
  • Low wear on the sleeve due to streamlining and laminar flow pattern.

Disadvantages of Pinch Valves

However, there are some disadvantages of pinch valves like

  • The pinch valve is not suitable for high-temperature applications as elastomeric material has a limitation on temperature resistance.
  • The rubber sleeve can collapse or deform on high-pressure differential and the valve may not open fully.
  • The pinch valve is not suitable for vacuum applications.
  • Not suitable for pulsating flow.