VALVES

Globe valve

It operates by reciprocating action of disc or plug. The disc or plug moves to or away from the seat thereby stopping the fluid flow or allowing the fluid to flow. The valve can be manually operated or power actuated or automatic actuated. Globe valves are available from 12 mm to 300 mm size and their temperature and pressure limits are 550 C and 150 kg/cm2 respectively. Material of construction for globe valve is carbon steel, stainless steel, ductile iron, brass, and other corrosion resistant alloys.

Gate valve

Gate valve functions by the reciprocating action of disc in its body. It can have a single disc or double disc. It is used for shut off operation. Gate valves are available in various sizes ranging from 12 mm to 300 mm and even more. Gate valve is light in weight, economic and offers low pressure drop. Conduit type gate valve is common in chemical process industries because it gives accurate flow control. Gate valve can be used upto 20 kg/cm2 and upto 675°C. Material of construction for gate valve is cast iron, carbon steel, stainless steel, ductile iron, bronze, nickel alloys etc. Rotating disc type gate valve with quick action lever actuator.

Ball valve

Ball valve has a spherical plug. The spherical plug is a controlling element. They are widely used in chemical process industries. It is used where throttling and shut off combination is required. It offers good flow characteristics. Ball valve consists of a two way globe and the ball rotates between resilient seats. It is available in venture pattern, reduced and full port patterns. The valve does not give good throttling. It can be available in size from 6mm to as large as 900mm. It can be used for pressures upto 500 kg/cm and temperature upto 300°C.

Butterfly valve

In butterfly valve the controlling element is a disc called as blade, vane or flapper, which rotates in horizontal or vertical direction and allows the fluid to flow. Butterfly valve is suitable for throttling or on-off operation at low pressure drop. It is economic, easy to install and does not allow the solids to build up. Butterfly value can be used for vacuum operations or pressures upto 80 kg/cm2. It is available in size ranging from 50mm to as large as 900 mm. The blade or flapper of a Butterfly valve can be made from rubber, neoprene, chloro sulphonated polyethylene etc.

Diaphragm valve

Main parts of a diaphragm valve are, body, bonnet and a flexible diaphragm. Diaphragm is lifted up when the valve is opened and the diaphragm is tightly pressed against the bottom of valve, when it is closed. Diaphragm valves are classified as: 1. weir type and 2. Straight through type. In some diaphragm valves, the diaphragm is not fully lifted up of the weir, so accurate control of small flow becomes possible. Diaphragm is made either from rubber, neoprine or buna. It is avalable in size 3 mm to as large as 600 mm. It can be used upto 20 kg/cm2 pressure and 2200 C temperature.Material of construction for diaphragm valve can be cast iron, stainless steel, and corrosion resistant alloys.

Plug valve

Plug valve is used for on-off service. It is the oldest type of valve. The main parts of a valve are body, plug and cover. Plug can be cylindrical or tapered. The plug has a slit cut in it to allow the fluid to flow. Plug valve can be made to have one or more openings to change the direction of flow. It can be lubricated or non-lubricated type. Lubricated plug valve is used in oil industry while non-lubricated valve is preferred where contamination is to be avoided. Plug valves are available in size from 6mm to as large as 750 mm. Lubricated plug valve can have high pressure rating upto 300 kg/cm2 and temperature rating upto 300°C.

Needle valve

Needle valve contains a plug. The plug is tapered and sits very accurately into the seat. The flow rate is regulated by the annular space between the tapered body of the plug and the seat. It is used for small and accurate flows. The valve size varies from 3mm to 25mm and can be used in the temperature and pressure range upto 260 C and 650 kg/cm respectively. Needle valves are used for controlling actuating air or hydraulic fluid, for reducing pressure fluctuations. Material of construction for needle valve can be bronze, brass, stainless steel etc.

Pinch valve

It can be used for on-off and throttling operations. The valve has a sleeve which is replaceable. It has low maintenance cost, low pressure drop and low initial cost. It can be used for handing slurries. Its operation mechanism is completely isolated from fluid. This eliminates problems of corrosion and contamination. Sleeves can be made of rubber or plastic. Pinch valve can be designed for pressures upto 20 kg/cm2, and temperature upto 250°C. Pinch valve is not suitable for vacuum operation.

Flush bottom valve

It has wide applications in process industries for discharging materials from tanks. It is available in size ranging from 25 mm to 150 mm. It can be used for discharging dry solid material from bins.

Solenoid valve

It is a control valve. Solenoid is applied to sliding stem, on-off globe valves. It is used for emergency shut off service requirements. It is available in size ranging from 1 mm to 100 mm. It can be used for absolute vacuum to very high pressures in the range of 650 kg/cm2 and temperatures as low as-250°C to 800°C. Material of construction for solenoid valve can be cast, iron, stainless steel, aluminum, plastic brass etc. Solenoid valves find wide applications in cryogenic operations.

Flow regulating valve

In a flow regulating valve a constant flow rate is maintained irrespective of any changes in the line pressure. As the pressure changes on either side of the stream, the diaphragm actuates a spring loaded valve. The spring loaded valve opens or closes maintains the flow at constant rate.

Y-type valve

In this valve the orifice is approximately at 42 to the path of flow. Y-type valve offers low pressure drop and good throttling condition.

Check valve

There are three types of check valves:

A. Swing check valve B. Piston check valve C. Lift check valve

It is used to prevent flow reversal. Fluid pressure keeps the valve open. It is closed either by back pressure
of fluid or by weight of the check system.

A) Swing check valve:

Swing check valve is used for low fluid velocities and where flow reversal is not frequent. Swing check valve can be used on the discharge side of pressure relief valve.

B) In lift check valve:

In lift check valve a disc, piston or a ball is used as a checking device. It can be installed in horizontal or vertical position. The fluid pressure raises or closes the disc or ball. Lift check valves are suitable where pressure drops are high. It is suitable for small pipelines.

C) Piston check valve:

Piston check valve is stem operated. It can be operated manually or by a motor. Check valves are available in sizes ranging from 6mm to 600 mm. They can be used for pressures upto 170 kg/cm2 and temperatures upto 675°C. Material of construction for check valve can be cast iron, steel, ductile iron, and corrosion resistant alloys.