Diaphragm Valve

In nearly every piping system, valve contributes as a basic engineering device.  These mechanical/electromechanical devices control media flow and come in many specific variants. There are many diaphragm valve manufacturers out there who provide proper valve as per your need. As this article focuses on the diaphragm valve, so we can look at what it is, how it operates, and the various forms that are available. This analysis could help to determine if diaphragm valves may be helpful and how to pick the proper version for the requirement. 

Diaphragm Valve

What is the diaphragm valve?

A diaphragm valve is a special kind of shut-off valve and is bi-directional in nature. Structurally distinct from the regular valves. As the name implies a diaphragm is the opening and closing element in a diaphragm valve which is made of a soft/flexible material which is elastic, non-corrosive, nonpermeable material such as rubber and plastic, this separates the fluid inside the valve body cavity from the cover cavity and the driving member which prevents contamination of the working medium and corrosion of operating parts.

For low pressure, low temperature, corrosive, and suspended materials application, diaphragm valves can be used. They benefit from the simplicity of the construction, strong and positive sealing, corrosion-resistance, and low fluid resistance, and as there is no leak path in design construction these valves considered leak-proof, this function renders the valve invaluable when the leakage within or out of the device cannot be accepted. All these benefits make the diaphragm valve popular and suitable for many applications.

How does the diaphragm valve work?

The working of a diaphragm valve is as simple as a pinch clamp valve. A resilient, elastic diaphragm is attached to the compressor by means of a diaphragm molded stud. When the operator wants the valve to be shut, the actuator is pressed and/or rotated and the membrane is forced into the edge of the firm damn, shutting the valve.

The compressor is moved up and down the stem of the valve. Thus, as the compressor is lifted, the diaphragm lifts. The diaphragm is pushed into the curved bottom or by the weir in depending upon the type of construction, as the compressor is lowered.

Types of the diaphragm valve

Two simple designs of diaphragm valves are mainly available: weir and straight-through. These valves operate the same way, but their body form, diaphragm, and application vary. To make the diaphragm valves acceptable for corrosive uses, the body interior and the end flanges should be lined. Various liner materials may be used, depending on the requirements.

1. By body structure:

• Wire type diaphragm valve.

The most common available designs are the weir-type diaphragm valve. The elevated lip/saddle configuration for limited flow control is ideally suitable and is safely leaked thanks to the cover over the diaphragm and actuator. This design is suitable for harmful or corrosive gas and liquids, as this cover keeps every breakdown of the membrane. As an integrated element of the valve body, a weir is given. The weir serves as the valve seat to compress the diaphragm to avoid the surge. The inclined body often naturally drains this valve, although it may occur in both directions and with certain uses, that might not be desirable. Generally, this type of diaphragm valve is manufactured in large sizes. The elevated weir decreases the amount of movement of the diaphragm from the completely open position to the completely closed position, thus decreasing the amount of strain and stress in the diaphragm. For smooth, homogenous fluids, the weir-type valve is often used, as viscous slurries and sediments can build up on either side of the saddle. In processes such as food/chemical, gas processing, corrosive, and water applications, they are most commonly found.

Wire Type Diaphragm Valve

• Straight through diaphragm valve.

The straight-through diaphragm valve is similar in appearance to the weir-types; but, it does not include the typical saddle and instead has a straight track. Usually, their membranes are more compact and allow for a longer distance to pass, since the very bottom of the valve must be touched. When the straight-through valve is open, for maximum streamline flow in any direction, the diaphragm lifts high. When the valve is closed, even with coarse or fibrous material in the line, the diaphragm seals tight for positive sealing. These valves must also be repaired because owing to their more compact membranes, their lifetime is normally shorter than weir-type designs. For slurries, viscous oils, and other conditions, where blocking must be minimized, straight through diaphragm valves are often used. In the beverage industry, the full-bore type of valve is most commonly used. It enables ball-brush cleaning, without opening or removing the valve from the line, with either steam or caustic soda. They are also suitable for bi-directional flow regimes since there is no saddle to avoid the sudden transition from inlet to outlet.

Straight Through Diaphragm Valve

2. By actuator.

• To decide what type of actuation to shut and open the valve should be used; this depends on the flow force and the wider structure of which the valve is a component. Manual, electric solenoid, pneumatic, thermal, hydraulic, and more modern actuators of the control mechanism provide actuation types.

Advantages of diaphragm valve:

• Diaphragm valves for the throttling service may also be used. Thanks to the wide shutdown area along the bench, the throttling features are those of a fast-opening valve.
• A weir-type diaphragm valve is suitable for regulating small flows.
• Give strong chemical resistance due to the range of lining available.
• Diaphragm valves are especially ideal for the treatment of contamination-free corrosive oils, fibrous slurries, toxic fluids, or other fluids.
• A diaphragm valve’s working function is not exposed to the media inside the pipeline. To mess with the working mechanism, sticky or viscous fluids may not come into the bonnet.
• Many fluids that might clog, erode, or spoil the operating parts of any other types of valves will move through the diaphragm valve without causing any trouble. Conversely, the lubricants used by the working mechanism cannot be permitted to contaminate the fluid being managed.
• There are no packaging glands to be protected and no chance of stem leakage in the valves.

Disadvantages of diaphragm valve:

• The weir will prevent the pipe from draining fully.
• The working temperatures and pressures of the diaphragm material are reduced. Pressures are typically limited to 200 psi and temperatures up to 400 F (204 C).
• The diaphragm can also decrease hydrostatic pressure.
• The diaphragm can suffer corrosion when used extensively in extreme throttling services containing impurities.
• Diaphragm valves are limited to small sizes, typically from 1⁄2 to 12 NPS (DN 15 to 300).

Diaphragm valve selection guide. 

Diaphragm valves do not have an industry-specific design; thus, determining the correct valve for your application could be tricky. This portion would include some crucial descriptions of the criteria to be defined. Note that this list is not comprehensive, but should at least guide the engineers or a diaphragm valve manufacturer in the correct direction.

• Valve Size: Since these valves are used in throttling applications, their size has major fluid effects. Firstly, calculate the desired amount of process fluid through the device to determine the correct size of the valve. This implies understanding the flow rate of the fluid, its particular gravity/viscosity, and the optimal flow rate. Second, measure the optimum temperatures and inlet/outlet pressures, as well as the valve’s desired potential and the forces it would require to obstruct the flow. The correct ratio of inner and outer diameter for your valve can then be calculated by using tables.
• Pressure drop range: What’s the optimal reduction in pressure through the valve? Ensure this value is defined, or if not sure, pick a sufficiently large percentage to adjust the fluid flow. Then decide the pressures the valve encounters as the device operates so that a valve that supports the whole range can be chosen.
• Actuation required: Using the previous portion, predict which type of diaphragm would be more useful for your process fluid. Then decide if the body and the stem will be revealed to the media or if these components should be isolated.
• Connection ends: Determine the relationship between the valve and your system; this may take the form of basic thread, welded joints, flanges, and/or other application-specific screening procedures. Next, evaluate the optimal material properties of the valve such that the fluid flow does not adversely affect the operation of the valve. For example, highly corrosive fluids need materials that do not decay in caustic conditions, such as stainless steel, bronze, and other metals. Finally, decide all other characteristics, such as unit, location indications, safety measures, and more to allow your valve to function better for your project.

Where is the diaphragm valve used?

A diaphragm valve is cheap, Effective, and comes in a variety of designs due to this it can be used in many applications. Some of the industries where it can be used are:

• Water treatment plants.
• Pharmaceutical industry.
• Food processing plants.
• Power plants.
• Vacuum services.
• Corrosion prone applications.

How to install a diaphragm valve.

• Remove the whole packaging material from the valve. Check the pipeline for contaminants and foreign objects before the installation and, if required, clean it.
• In any mounting location, the valve may be installed. Care should be taken to provide entry to the valve from both directions for service. When the valve is mounted in the open field, it must be secured from direct weather impact at the site.
• The gap between the pipeline flanges should be at least 20 mm above the complete length of the valve during the installation of the valve, so as not to affect the operating strips and to allow the gaskets to be installed. As flange joints are recommended with steel-enhanced rubber joints, this is critical for slip-on flanges.
• The counter flanges of the piping have to be plane-parallel and concentric. Link bolts should be fixed similarly crosswise (without tension).
• The pipeline must not be elevated to the valve by any means whatsoever. For corrosive media, flat gaskets must be used in compliance with DIN 2690.

Maintenance of diaphragm valve:

• All high-pressure lines must be lowered and protected against re-start before beginning maintenance work! Both connections must be tested for leakage and tightness after completion of the repair works.
• Diaphragm valves are often maintenance-free. The lubricant nipple sort at the covering neck should be lubricated at frequent intervals.
• Inspection: Find out the exterior condition of the valve. Clean and patch the coating if necessary. Check the tightness of the pipe contacts, e.g., the flanges. Test the smooth operation of the valve. Switch over the entire stroke manually. Check the tightness at the end of the seal: adjust the valve to a closed position. Check the decrease in pressure downstream and upstream of the valve.
• Elastomer diaphragm should be observed while it is stored: the storage space should be cold, dry, and adequately ventilated. A room temp. of between +20 0 C and-10 0 C must be preserved. When the storage space is heated, the radiators and drains must be shielded from the storage containers. The distance between the heater and the storage products should be at least 1m. Approximate relative humidity. 65% has a beneficial effect on preserved diaphragms. The diaphragm should not be exposed to clear daylight. Solvents, oils, and lubricants should not be packed together with diaphragms of the elastomer. Separate new stored diaphragms from longer stored diaphragms. Often use the longer retained diaphragms first.
• Cleaning of Diaphragm: Rubber items should be washed with hot water. After a storage time of 6 to 8 months, it is advised to clean and rinse with water before installation with a 1.5 percent sodium carbonate solvent. Cleaned diaphragms could not be dried by the heater.
• Unscrew cover the bolts crosswise and raise the top off of the body. The adhesive between the body cover flange and the diaphragm can be separated by going back and forth. If it is difficult to remove the top, the valve can be pushed in the closing direction by means of a handwheel, which raises the cover and enables the valve to be withdrawn along with the diaphragm.
• Unclamp diaphragm by clockwise rotation of the pressure component. Remove the pipe protection (rubber hose) from the new diaphragm. Screw the diaphragm with the diaphragm screw fully into the pressure part.

Summary: As we have discussed above the diaphragm valve is suitable for many applications as it is simple, cost-effective, and has very little maintenance. This article briefly guides you all about the diaphragm valve.