Actuated Diaphragm Valves
The Construction of a Diaphragm Valve consists of a rigid body cast or forged in Bronze, Stainless Steel (316), Cast Steel, Alloy 20 CN7M, Monel, Hastelloy, or Ductile Iron in sizes (1/2” thru 12”) with a weir placed in the flow path (Weir type) or unobstructed flow path (Straightway), with a flexible diaphragm at the center, a compressor which is used to force the diaphragm against the weir, and the bonnet, which when actuated, is termed an air motor. An air motor is a pneumatic actuator that must be sized in relation to the valve size, service media in the valve, available air pressure to actuate the air motor, and the pressure of the service media passing through the valve.
Other contingencies to consider are whether the valve requires a Teflon diaphragm, is there a plastic lining? What is the service media and service temperature?
Diaphragm valve linings, including rubber linings, are Glass Lined, Soft Rubber, Hard Rubber, Butyl Lined, Hypalon Lined, PVC Lined, PP Lined (FDA), Tefzel Lined and PVDF* Lined (FDA). Diaphragm valve metal body materials are CI, Cast Iron, DI Cast ductile iron, FS Forged steel, CS Cast steel, Alloy 20 CN7M, Bronze, M35 Monel, and Hastelloy C. Thermoplastic bodies are made in solid PVC, CPVC, PVDF, Kynar, and Polypropylene. These material options are a factor when choosing a diaphragm valve actuator.
Weir type versus Straightway diaphragm body selection is a function of the service media or viscosity. A valve body suitable for abrasive service uses a Straightway design, where suspended solids or slurry media is present. The compressor is pressed against the Straightway valve body, not the valve weir. Since the seat does not press against the weir, the port allows the straightway body full flow. Weir valve services are more popular for pressure and temperature variants. They are used to control caustics or acids or elevated temperatures in fluids that are used in pharmaceutical, chemical processing, food processing, water treatment , and high purity applications. Manual operation by handwheel adjusts the liquid control to prevent leaks or reduce flow in throttling valve service.
The valve body can vary according to space or cost. PVC and CPVC socket weld valves offer a cost-effective alternative to valve characteristics normally associated with a valve body made of exotic metals like Alloy 20 CN7M, Monel, or Hastelloy. The industry standardization society has codified diaphragm valves for face-to-face dimensions, PVC and CPVC socket weld , and NPT threaded end lengths and flanged body dimensions. Note, plastic linings like PVC and CPVC has a different take-out dimension than say, glass-lined valves, or solid PVC and CPVC flanged valves. See our literature on valve body selection at www.authorizedparts.com
Consult our corrosion resistance guide for material selections.
Diaphragm Valve Actuator Types
Actuated diaphragm valves are available as pneumatic and electric actuators, open and closed position, or spring-loaded. Electric actuators have NEMA Code requirements. Spring operated valves must specify fail open or fail closed operation. Actuated valves can be equipped with a solenoid valve to signal a pneumatic actuator to change valve position.
Typically an actuator on a diaphragm valve is called an air motor. There are three basic types of air motors: Fail Open, which is Spring-to-Open, Air-to-Close, which often uses a normally closed 3 way, 2 position solenoid valve that closes when de-energized and the valve opens. The valve will fail open with the loss of electrical power to the solenoid valve.
Fail Closed air motors, which are Spring-to-Close, Air-to-Open is the opposite of the Fail Open type.
The operation uses a normally closed 3 way, 2 position solenoid valve. When the solenoid is energized, the valve opens and when de-energized, the valve closes. The valve will fail closed in the event of loss of electrical power to the solenoid valve.
Double Acting air motors are Air-to-Close, Air-to-Open. This type of actuator uses a 4 way, 2 position solenoid valve. There is no fail position.
Diaphragm Valve Air Motor Accessories
The three basic types of air motors can be accessorized with mechanical and electrical options. Mechanical Accessories allow for greater flow control for metering or throttling of services. Adjustable Opening Stop, Adjustable Travel Stop, Wrench Opening Device, Handwheel Opening Device, Adjustable Opening Stop, Handwheel Opening Devices can be added to the air motor in conjunction with electrical instrumentation such as solenoid valves, limit switches, position indicators, valve positioners, and proximity switches.
Air Motor Sizing
Selection of the correct air motor or actuator is a function of the following factors:
Line Pressure is the service media pressure in the pipeline against which the actuator must close.
Pressure Drop: 100% – when the actuator is closed, then pressure is applied or 0% – when the actuator needs to shut the valve off against the line pressure.
Operating Pressure is the air pressure required to power the actuator.
Valve Size is the nominal size of the valve body (2”, 4”, etc.) in inches.
Valve Type, either weir type or straightway
Diaphragm Type: PTFE-faced diaphragms are more rigid and require higher operating pressures.
When these factors have been determined, choose the appropriate actuator from the performance graphs available in our reference guides.
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Actuator Spring Sizing
Available Operating Pressure, the air pressure required to power the actuator, may on occasion below, or abundantly available, permitting economy by way of using a small actuator with an oversized spring, or conversely, a large actuator with an undersized spring. The spring in any diaphragm valve actuator requires the force on the stem equal to zero. The formula is generally calculated using the following input: the area of the diaphragm, operating air pressure, spring constant, spring displacement, and process pressure drop at shut-off pressure. The force of the acting air is in a positive direction (direct acting) and is opposed by spring compression force and force due to process flow. Air consumption, the operating pressure of instrument air is a cost factor in installations. Ample air at adequate pressure to produce stroke speed and movement is concerned, which will determine the air volume and consumption of the air motor. The delta factor is the sole determinant in spring size, thereby allowing for, in some cases, the economy of air motor size.
Valve body Selection
For weir-type diaphragm valves, valve body selection is a function of the corrosiveness of the service media or the viscosity. For example, a valve body suitable for abrasive service, typically, the construction is the Straightway design, where suspended solids or slurry media is involved. The compressor is pressed against the valve body, not pressed against the valve weir. Since the seat does not press against the weir, full access to the port allows the straightway valve body full flow, best suited for solids. Weir valve services typically involve pressure and temperature considerations as well. These valves can be used to control caustics or acids involving other types of weir type diaphragm valve account for pharmaceutical flow control, for example, used in chemical processing, food processing, water treatment, and high purity applications. Manual operation is ideally suited for handwheel-adjusted liquid control to prevent leaks or reduce flow in a metering valve service.
The valve body can vary according to space or cost. PVC and CPVC socket weld valves offer a cost-effective alternative to valve characteristics normally associated with a valve body made of exotic metals like Alloy 20 CN7M, Monel, or Hastelloy. The industry standardization society has codified diaphragm valves for face-to-face dimensions, PVC and CPVC socket weld, and NPT threaded end lengths and flanged body dimensions. Note, plastic linings like PVC and CPVC have a different take-out dimension than say, glass-lined valves, or solid PVC and CPVC flanged valves. See our literature on valve body selection at www.authorizedparts.com
Flow control considerations
Weir and Straightway valves come in all configurations and sizes based on the application and the fluid in the piping. Flow control, either unimpeded flow control or regulated flow control, is the first consideration. Some valves are operated manually or actuated. The speed of the actuator or the turn of a handwheel will adjust product flow. Actuated diaphragm valves can carry pneumatic and electric actuators, both open and closed positions, or spring-loaded actuation. Electric actuators must specify operating voltage and NEMA Code requirements. Spring operated must specify fail open or fail closed operation. Actuated valves can also be assisted with a solenoid valve to signal a pneumatic actuator to modify the valve position.
Typically an actuator on a diaphragm valve is called an air motor.
The diaphragm seal is critical to the life of the valve. The pressure rating of a valve body is only as high as the pressure rating of the diaphragm material itself. This lowered pressure characteristic of my affect flow control. Caution should be made when selecting the diaphragm, valve seat, and seals. When selecting elastomeric diaphragm materials, be certain that the valve compressor mates with the stud on the diaphragm. Teflon-faced R2 and TM diaphragms utilize a tube connector, which is a different compressor than that used for diaphragm materials made of Hypalon, EPDM, BUNA – N, Natural Rubber, Neoprene, and Viton.
How to Specify or Order an Actuated Diaphragm Valve
Details of operating conditions should be outlined as a starting point for specifying an actuated valve. Also, what functions do you wish the valve to perform?
Choose the body material, connection type, size, and valve orientation, and diaphragm type. For air motor sizing choose one of the three basic types. Include pneumatic factors for instrument air, line media pressure, and any additional relevant details or options.
Submit your RFQ on Authorized Parts website easy to use form at: https://www.authorizedparts.com/request-a-quote-2/
How to Order an Actuated Diaphragm Valve replacement parts
Air motor and actuator parts, and diaphragm valve parts are easily replaceable. Provide the make and model of the valve, size, and the name of the part: Compressor, Air Motor Diaphragm, Body, Diaphragm, Spindle, Actuator spring, etc., and Authorized Parts, Inc. with providing a part number and a quote. See our chart for selecting elastomeric diaphragm materials and compressor connections. Teflon-faced R2 and TM diaphragms utilize a tube connector, Hypalon, EPDM, BUNA – N, Natural Rubber, Neoprene, and Viton used a threaded connector.
Yes. Actuated diaphragm valves are made with both pneumatic and electric actuators for open and closed positions or spring-loaded actuation. Electric actuators must specify operating voltage and Code requirements. Spring operated must specify the spring torque, and fail open or fail closed operation. Solenoid valves, positioners, and limit switches can be added for incremental flow control and position.
Yes. All valve testing requirements can be made available for Lined Valves and Fittings. MTR’s, NDE, Pressure Testing, Radiography Testing, Magnetic Particle, Dye Penetrant, PMI, Positive Material Identification, Hardness Testing, and Failure Analysis.
No. The rate of the valve is influenced by the diaphragm material. The hydrostatic test pressure must not exceed the maximum pressure rating of the diaphragm.
Generally speaking, Yes. Manufacturer’s valves tend to cross-reference to one another. Grinnell, Saunders, ITT Dia-Flo, Dow, Resistoflex, and Crane are examples of manufacturers with equivalent products. However, not all design features are the same, so care should be taken when evaluating.