The difference between diaphragm valve and globe valve

The difference between diaphragm valve and globe valve

1 globe valve

A globe valve is a valve with a closing piece (disc) moving along the center line of the seat. According to this form of movement of the valve disc, the change of the valve seat port is proportional to the stroke of the valve disc. Because the stem opening or closing stroke of the stop valve is relatively short, and has a very reliable cutting function, and because the change of the valve seat port is directly proportional to the stroke of the valve disc, it is very suitable for the adjustment of the flow rate. As a result, this type of valve is ideal for cutting or regulating as well as throttling.

Advantages:

① In the opening and closing process, because the friction between the disc and the valve body sealing surface is smaller than that of the gate valve, it is wear-resistant.

② The opening height is generally only 1/4 of the valve seat channel, so it is much smaller than the gate valve;

(3) Usually there is only one sealing surface on the valve body and valve disc, so the manufacturing process is better and easy to maintain.

④ Because its filler is generally a mixture of asbestos and graphite, it has a higher temperature resistance grade. General steam valves use stop valves.

Because the flow direction of the medium through the valve has changed, the minimum flow resistance of the stop valve is higher than that of most other types of valves;

Due to the long stroke, the opening speed is slower than the ball valve.

2. diaphragm valve

Diaphragm valve refers to a flexible film or combined diaphragm installed in the valve body and valve cover, and the closing part is a compression device connected with the diaphragm. The seat can be weir shaped, or it can be the wall of the straight flow channel.

The structure of the diaphragm valve is very different from the general valve, is a special form of truncation valve, its opening and closing parts is a diaphragm made of soft material, the valve body cavity and the valve cover cavity and drive parts are widely used in various fields.

Commonly used diaphragm valves are rubber lined diaphragm valves, fluorine lined diaphragm valves, unlined diaphragm valves, plastic diaphragm valves. The diaphragm valve has the advantages of simple structure, small fluid resistance and large flow capacity compared with other types of valves of the same specifications. No leakage, can be used for the adjustment of high viscosity and suspended particles medium.

The diaphragm isolates the medium from the upper chamber of the valve stem, so the medium will not leak out without packing. However, due to the limitations of the diaphragm and lining materials, the pressure resistance and temperature resistance are poor, and are generally only suitable for 1.6MPa nominal pressure and below 150 ° C.

The flow characteristic of diaphragm valve is close to the fast opening characteristic, and it is approximately linear before 60% stroke, and the flow rate after 60% does not change much. Pneumatic diaphragm valves can also be equipped with feedback signals, limiter and positioner devices to meet the needs of automatic control, program control or flow regulation. The feedback signal of pneumatic diaphragm valve adopts contactless sensing technology. The product uses a thin film propulsion cylinder instead of the piston cylinder, eliminating the piston ring is easy to damage, resulting in leakage and resulting in the failure to push the valve opening and closing.

When the air source fails, the handwheel can be operated to open and close the valve. The diaphragm valve replaces the spool assembly with a corrosion-resistant lined body and a corrosion-resistant diaphragm, which uses the movement of the diaphragm to regulate.

The valve body material of the diaphragm valve is cast iron, cast steel, or cast stainless steel, and is lined with a variety of corrosion-resistant or wear-resistant materials, diaphragm material rubber and polytetrafluoroethylene. The diaphragm of the lining has strong corrosion resistance and is suitable for the regulation of strong corrosive media such as strong acid and alkali

Advantages:

① The control mechanism is separated from the medium path, not only to ensure the purity of the working medium, but also to prevent the possibility of the medium in the pipeline impacting the working parts of the control mechanism, the valve stem does not need to use any form of separate seal, unless it is used as a safety facility in the control of harmful media;

② Because the working medium is only in contact with the diaphragm and the valve body, both of which can use a variety of different materials, the valve can ideally control a variety of working media, especially suitable for media with chemical corrosion or suspended particles.

The structure is simple, only composed of three parts: valve body, diaphragm and valve cover assembly. The valve is easy to remove and service quickly, and the diaphragm can be replaced on-site and in a short time.

Due to the valve body lining process and diaphragm manufacturing process and restrictions, larger valve body lining and larger diaphragm manufacturing process are difficult, so the diaphragm should not be used for larger pipe diameter, generally used in DN≤200mm pipe.

Due to the limitation of the diaphragm material, the diaphragm valve is suitable for low pressure and low temperature occasions. Generally not more than 180℃;

The adjustment performance is relatively poor, only in a small range of adjustment (generally closed to 2/3 opening, can be used for flow adjustment).

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