Diaphragm Valves

Diaphragm valves are divided into two main groups, diaphragm control valves, which allow manufacturers to modify flow and pressure rates and diaphragm check valves, which ensure the unidirectional flow of materials. Within these two main categories, these instruments can be one of two configurations. Seat valves are used when a nonlinear stream path is needed while the weir valve offers linear regulation. Each has two or more ports. Materials flow in through one port and out the other when the valve is not engaged. When an actuator is used to stretch the membrane of the valve, however, flow is limited or completely inhibited. The ease and reliability of these valves makes their use common in such variable industries as biopharmaceutical, agriculture, irrigation, plumbing, medical, water treatment, chemical and food processing, pulp and paper, mining and energy production. Several of these applications require the use of biotech valves, hygienic valves or sanitary diaphragm valves in order to avoid product contamination, which is also significantly reduced by using zero static valves which eliminate opportunities for flow stagnation and bacterial growth. Medical, chemical and food processing industries in particular reap the benefits of stainless steel and plastic diaphragm valves which are easily sterilized. The actuation device also plays a role in the capabilities of clean valve operation. The variable types of engagement include manual, automated, electric, hydraulic and pneumatic diaphragm valves, each of which broaden the possibilities of diaphragm use and installation.

The two most common types of diaphragm valves are seat valves and saddle valves. Also known as straight-way and weir valves respectively, these devices each have two or more ports, one for inlet and one for exhausting the process stream. The main difference is the alignment of the ports. The seat valve body exhibits a 90 degree bend which causes a change in the directionality of the process stream as it moves around the corner. Alternatively, the saddle type diaphragm valve employs a linear approach with the two ports being located directly opposite each other. Both types are used in a broad array of industries though seat valves are more often employed in tank or cistern bottoms that require the angled flow. Weir valves are often installed into pre-existing flow lines. Despite this variation, the appearance and construction of both types of valves is remarkably similar except for the bend in the piping or tubing. A cylindrical or spherical body is attached to the tank or tubing in which the valve is needed. This body houses the actuation device. At the bottom of this cylinder is the diaphragm. The diaphragm is thick in the middle and thinner at the edges to allow for easy stretching. When the valve is open, the diaphragm is lifted up allowing fluids or gases to pass. When the valve is closed, the actuator engages a rod or piston known as the stem. This stem applies pressure to the diaphragm, pushing it towards the opposite wall of the piping. This creates a flexible barrier and effectively blocks the materials in transit.

Actuation devices range considerably to provide hydraulic, electric, manual and pneumatic controls. Pneumatic is among the most common type of automated diaphragm valve as it requires only the use of compressed air to expand and contract the diaphragm materials. These materials must be durable and chemically compatible with the process stream. Common body materials include brass, stainless steel, cast iron, steel, PVC and CPVC among others. In some instances the body is lined with rubber or fluorine plastics to increase product longevity and reduce friction. The diaphragm itself is made of elastomers similar to those used to line the valve mechanism such as polypropylene and polyethylene. Often when highly abrasive materials are in use, the diaphragm will be reinforced the mesh fibers. Common process stream compositions include adhesives, silicones, water, chemicals, cleaners, sanitizers, coatings, paint, fuel, coolants, colorants, paints and more. Selecting the proper materials for a given task will help to improve product longevity and functionality. Incompatible materials can cause serious damage to the valve and can lead to product contamination.

With so many different possibilities, it is important to understand the needs of specific applications before purchasing and installing a diaphragm valve. Manufacturers and retailers can provide helpful insight on the capabilities of a specific valve as it relates to industrial and commercial uses. Common considerations include media type, temperature and pressure ratings, frequency of operation, diameter and other dimensions, required end connections and process stream velocity. Proper installation of a suitable diaphragm valve provides a reliable and leak-proof addition to any plumbing or material transport operation. Valve cleaning and maintenance is simple and generally inexpensive. The superior performance of diaphragm valves is well known making it popular in a number of industrial manufacturing applications.

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Types of Diaphragm Valves

• Biotech valves are intended to be used in the biotechnology fields — agriculture, food science, pharmaceuticals and medicine. Biotech valves must be sanitary.
  
• Diaphragm check valves are process stream regulation devices that maintain the unidirectional flow of a system through the use of a flexible membrane.
• Diaphragm control valves employ a membrane or elastomer film to regulate the process stream of various manufacturing operations. Everything from rate, pressure and temperature to liquid level can be regulated with the application of these valves.
• Diaphragm diverter valves can be used to divert flow from an inlet to two or more outlets; they can also be used in reverse to feed flow from one line into two or more lines.
• Diaphragm tank bottom valves are designed for use at the bottom of a tank or vessel, to drain or sample from the tank.
• Diaphram valves, more properly known as diaphragm valves, are inline devices that utilize a membrane to transect a pipe completely or partially in order to regulate the flow of liquid, gaseous or semi-solid process streams.
• Hygienic valves are specially designed to be used in sanitary and aseptic (sterile) applications.
  
• Plastic diaphragm valves are process stream regulation devices that use an elasticized polymeric membrane to transect conduits either fully or partially as needed to maintain optimal flow and pressure rates. Included in this material category are those diaphragm valves made entirely of plastic components as well as those that employ plastic elements in conjunction with metal parts and forms.
• Pneumatic diaphragm valves convert the energy of compressed air in order to engage an elastomeric membrane thereby maintaining and regulating the flow of a given process stream.
• Process valves include any type of mechanical device that can stop, start or regulate the flow of liquid, gas, solid material or steam.
  
• Sanitary diaphragm valves are process flow regulation devices constructed of sterile materials and designed to create an aseptic environment for liquid, gaseous and semi-solid material flows. 
• Tank bottom valves are designed to eliminate deadlegs or areas where bacteria might become trapped in the valve.
• Weir valves have a raised section, or "weir," on which the diaphragm presses to create a seal.
  
• Zero static valves are multi-port diaphragm valves that serve to promote drainage and eliminate dead-leg, or process stream stagnation. These valves accomplish both measures not only by reducing the number of recesses where materials may be caught, but also providing and exhaust or purge port for materials that do become trapped.

Diaphragm Valve Terms

Actuators - Controls that switch the position of a valve from open or partially open to partially or completely closed. Actuator operation may be manual, pneumatic or hydraulic.

Backpressure - The pressure at the outlet of a relief valve, caused by pressure in the discharge system. Pressures may be constant or variable.

Bellows - A sealing device that prevents leaks between the valve stem and the body of the valve.

Bonnet - A cover fitted over the valve body, which may be removed for valve maintenance.

Cracking Pressure - The pressure at which leaks start to flow through a valve.

EPDM - Ethylene propylene diene monomer. EPDM is a commonly used rubber seal material that is compatible with many chemicals.

Flange - A type of pipe fitting that attaches with nuts and bolts.

Flare - A pipe fitting that uses a socket and a union nut to form a connection. Flares are one of the most crevice-free pipe fittings and may be used for ultrapure processes.

GPM - Gallons per minute. Used to measure flow through a pipe, valve, inlet or outlet.

O-ring - A rubber seal with an "o" shape, used to seal connections between pipes and valves.

Ports - Passages that allow flow into and out of a valve.

Set Pressure - The pressure from an inlet that a valve is adjusted to open, maintain or control under service conditions.

Stem - A rod that spans the inside and outside of a valve, transmitting motion to control the internal disc, which moves to seal or unseal the valve.

U-cup - A seal formed into a u-shaped channel. This type of seal may be used when an O-ring is not desirable.