Control Valve

What is a bleed valve and what does a bleed valve do

A bleed valve is a valve that is used to isolate the flow of the fluid or air. Bleed valves are mostly used in many industrial applications such as piping systems and in heavy-duty gas turbines. The inlet of the bleed valve will be small so that it can restrict the flow of air or liquid. The major purpose of the bleed valve is isolation, but it also interferes with the system process when it is required. There is a rated speed for the bleed valve to stay open. So bleed valves are able to provide tight shut-off or isolation for example in some industrial processes there could be harmful gases and the bleed valves would prevent the emission of the harmful gas. In many industries compressor, bleed valves are used in gas turbines and it protects the axial compressor against the surging and stalling that could happen while the starting and stopping the process. Bleed valves are also used to take the liquid or air from one system and then it will be sent to another system.

What is a double block bleed valve and what is the purpose of double block bleed valve

This valve can be considered as a combination of two ball valves and a needle valve. The needle valve will be present between the two ball valves. Double block bleed valves provide zero leakage so that the maintenance and repair can be done very quickly. So the double block bleed valves are used in many applications. These valves are used in some fueling systems because this valve can ensure zero leakage.

What are the characteristics of double block bleed valve

  • It can provide tight-shut off so there won’t be any leakage
  • There is no need to use spring or any other part to do the sealing, the seals are mechanically energized
  • During the opening and closing, there is no friction, because during the rotation there is no contact between the slip seals and the seating ring
  • No need for lubrication

How does a double block bleed valve work

These valves are used in many industrial applications so that they can provide better isolation while doing plant operations. Double block bleed valves are mostly used in industrial systems that require proper isolation and these valves are used for critical applications such as for high-pressure systems and the industrial process that has toxic gas. These valves have two seating surfaces and it can block the upstream and downstream side of the valve. These valves are widely used in the pipeline and process system to provide isolation. The individual seal would be fully isolating when the valve is in a closed position and thus it won’t allow any flow from the downstream and upstream. During the overpressure, the body cavity would bleed because of the thermal relief vent, and because of this, the downstream pipeline would be isolated from the upstream pressure.

What is positive isolation and how is it done

Positive isolation is a process of isolating a section of the plant from the operating section. It can also be considered as isolating equipment from the operating section and the equipment could be pressure indicators and level gauges. The two-block valve would be closed. The bleed assembly and the shutdown side would be drained. The bleed in the double-block and bleed assembly is used to relieve the trapped fluid from space between two block valves.

What is a DIB

DIB is a double isolation bleed valve, it is a single valve with two seating surfaces. The two seating surfaces would provide a seal against pressure from a single source. And thus it would go the cavity between the seating surface

How to select a bleed valve

  • It must be selected according to the pressure level
  • Seal integrity
  • Isolation stability
  • Monitoring capability
  • Restraint integrity
  • Vibration
  • Maintenance
  • Size
  • Isolation

What are the applications of double block bleed valves

  • It is used in automatic shutdown systems
  • Gauge isolation
  • Instrument drain
  • Sampling connection
  • Pressure measurement
  • Piping and instrument interface


post-graduate in Electronics & communication.

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