What is a Diaphragm Valve?

The Diaphragm valve is a diaphragm as the opening and closing parts close the flow path, cut off the fluid, and the valve body cavity and bonnet cavity separated from the stop valve. The structure of the diaphragm valve is very different from the general valve, is a new type of valve, and is a special form of stop valve, its opening and closing parts are a piece of soft material made of diaphragm, the valve body cavity and the bonnet cavity and drive parts separated, is now widely used in various fields. ATO.com will introduce the basics of the diaphragm valve, which will help the user in the use of the diaphragm valve more simple and convenient.

Introduction

A diaphragm valve is equipped with a flexible diaphragm or a combination of diaphragms in the valve body and bonnet, and its closing member is a compression device connected to the diaphragm. The valve seat can be a weir or a pipe wall in a straight flow path. The advantage of the diaphragm valve is that its manipulation mechanism and the media pathway are separated, not only to ensure the purity of the working medium but also to prevent the pipeline medium impact on the manipulation mechanism of the possibility of working parts.

In addition, no separate seal of any kind is required at the valve stem, except as a safety feature in the control of hazardous media. In diaphragm valves, since the working medium comes into contact only with the diaphragm and the valve body, both of which can be made of a wide range of different materials, the valve is ideal for controlling a wide range of working media and is particularly suitable for media with chemically corrosive or suspended particles.

Diaphragm valve operating temperature is usually limited by the diaphragm and valve body lining materials used, its operating temperature range of about -50 ~ 175 ℃. The diaphragm valve structure is simple, only by the valve body, diaphragm, and valve head assembly of three main components. The valve is easy to disassemble and repair quickly, and replacement of the diaphragm can be accomplished on-site and in a short period.

Structure Classification

Diaphragm valves can be divided into six types according to structural form: house type, direct flow type, cut-off type, straight-through type, gate type, and right angle type. The connection form is usually a flange connection. The driving mode can be divided into manual, electric, and pneumatic three, and pneumatic drive is divided into normally open, normally closed, and reciprocating three.

1. Right-angle Type: also known as protruding edge type, is the most basic one commonly used code (G41). Its valve body is lined. The diaphragm valve body lining is to better utilize its corrosion resistance characteristics. This type of structure, in addition to the straight-through type, can also be made into a right-angle type.
2. Roof Type: its structural shape is similar to the globe valve, this form of diaphragm valve, fluid resistance than the right-angle diaphragm valve, but the sealing area is large, sealing performance is good, can be applied to the pipeline with a high degree of vacuum.
3. Straight-through: its structural form is similar to the gate valve, gate type diaphragm valve fluid resistance is minimized, suitable for conveying viscous materials. Diaphragm materials commonly used natural rubber, neoprene rubber, butyl rubber, butyl rubber, isobutyl rubber, fluorinated rubber, and polyfluoroethylene propylene plastic (F46).

Working Principle and Composition

Diaphragm valve with corrosion-resistant lining of the valve body and corrosion-resistant diaphragm instead of the spool assembly, using the movement of the diaphragm to regulate. Diaphragm valve body material using cast iron, cast steel, or cast stainless steel, and lined with a variety of corrosion-resistant or wear-resistant materials, diaphragm material rubber, and PTFE. Lined diaphragm corrosion resistance, suitable for strong acid, strong alkali, and other strong corrosive media regulation.

Diaphragm valve structure is simple, with smaller fluid resistance, and flow capacity than other types of valves of the same specification; no leakage, and can be used for high viscosity and suspended particles of the medium regulation. Diaphragm to isolate the medium and the upper cavity of the valve stem, so no packing medium will not leak. However, due to the limitations of the diaphragm and lining materials, pressure resistance, and temperature resistance are poor, and generally only apply to 1.6MPa nominal pressure and 150 ℃ below.

Diaphragm valve flow characteristics are close to the fast-opening characteristics, in 60% of the stroke before the approximate linear, 60% of the flow after the change is not significant. A pneumatic form of diaphragm valve can also be attached to the feedback signal, limiters positioners, and other devices to adapt to self-control, program control, or adjust the flow rate needs. The feedback signal of the pneumatic diaphragm valve adopts non-contact sensing technology. The product adopts a membrane-type propulsion cylinder, instead of a piston cylinder, which excludes the disadvantage that the piston ring is easy to be damaged, resulting in leakage and not being able to push the valve to open and close. When the gas source fails, you can still operate the handwheel to open and close the high precision diaphragm valve.

Diaphragm Valve Sealing Principle

The diaphragm valve sealing principle relies on the operating mechanism of the downward movement of the diaphragm or diaphragm combination with the weir-type lined valve body or through the lined valve body of the channel to close, to achieve sealing. The size of the sealing pressure is realized by the size of the downward pressure of the closing member. As the valve body can be lined with a variety of soft materials, such as rubber or PTFE, etc., the diaphragm is also made of soft materials, such as rubber or synthetic rubber lined with PTFE, so with a smaller sealing force can achieve a complete seal.

The diaphragm valve has only three main parts of the valve body, the diaphragm and valve cover assembly. The diaphragm separates the inner cavity of the lower valve body from the inner cavity of the upper bonnet, so that the valve stem, stem nut, valve flap, pneumatic control mechanism, electric control mechanism, and other parts located above the diaphragm do not come into contact with the media, and will not produce media leakage, eliminating the sealing structure of the stuffing box.

Characteristics

• Fluid resistance is small and suitable for corrosive, viscous, slurry media.
• Can be used for the medium containing hard suspended matter, because the medium is only in contact with the valve body and the diaphragm, so there is no need for a stuffing box,
• there is no stuffing box leakage problem, no corrosion of the valve stem part possible.
• Can not be used for higher-pressure occasions. The disadvantage of the diaphragm valve is not high-pressure resistance, generally within 6kgf/cm2 (0.6MPa). Temperature resistance is also limited by the diaphragm, generally only 60 ~ 80℃, the highest (fluorinated rubber) does not exceed 180℃.

Diaphragm Valve Applicable Occasions

• Diaphragm valve is a special form of cut-off valve, the opening and closing parts are a piece of diaphragm made of soft material, which separates the inner cavity of the valve body from the inner cavity of the valve cover.
• Due to the limitations of the valve body lining process and diaphragm manufacturing process, a larger valve body lining and larger diaphragm manufacturing process is difficult, so the diaphragm valve should not be used for larger pipe diameter, generally used in≤DN200 following the pipeline.
• Due to the limitations of the diaphragm material, the diaphragm valve is suitable for low-pressure and low-temperature occasions. Generally do not exceed 180 ℃. Because the diaphragm valve has good anti-corrosion properties, it is generally used in corrosive media devices and pipelines. Due to the use of diaphragm valve temperature applicable media by the diaphragm valve body lining material and diaphragm material limitations.

An in-depth understanding of the design, principle, and application of the diaphragm valve, found that it is important and widely used in various industrial fields. Diaphragm valves, with their unique structure, play an irreplaceable role in fluid control, effectively isolate the medium, and ensure the reliable operation of the system. The study of diaphragm valves, makes us realize more deeply that diaphragm valves in today's industry are not only a kind of equipment but also an engine to promote technological innovation and production progress.