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Zwick TRI-CON Butterfly Valve
Thu 18 Jan 2018

What are double block and bleed valves?

Double block and bleed valves are used for high-pressure systems or toxic/hazardous fluid processes. In this blog, BM Engineering Supplies explain what double block and bleed valves do and how to operate them safely.

How does a double block and bleed work?

A double block and bleed valve is used for positive isolation of process fluids from other pieces of equipment. It will usually be formed by two block valves and a bleed valve. When the process fluid feeds the downstream equipment, the valves are set up to have the isolation valves remain open and the bleed valve closed. On the other hand, when the downstream equipment is isolated from the process fluid, the valves are then set with the isolation valves closed and the bleed valve open.

If one of the isolation valves was to be accidently opened, or were to leak, the fluid would be prevented from flowing by the secondary isolation valve. Because of this, there should be no pressure collection because the material or leakage will flow through the bleed valve.

Functions of double block and bleed valves

There are many useful functions of double block and bleed valves. As well as being able to stop material flow in automatic shutdown systems, they are also able to provide isolation of hazardous temperatures, materials or pressure whilst equipment maintenance or temporary shutdown is active. Isolation is also an advantage of these valves as they are able to isolate both steam heat from a batch process and have the ability to isolate process material feeds that are required for some operations.

Double block and bleed safety

As double block and bleed systems are used in a variety of different operations, it is important to know the systems and how to use them safely. The first thing you should do is learn how to properly operate a manual double block system, learning how to close and open valves in the right order. It is also vital to know if the bleed should be closed, plugged or left open for all double block and bleed systems. Another thing to remember is when using automatic safety shutdown systems, make sure that the bleed is not plugged as this is often forgotten.

Zwick butterfly valves

We often use Zwick butterfly valves for double block and bleed installations. BM Engineering can supply a number of butterfly valves from Zwick, designed for reliable functionality and 100 per cent zero-leakage in critical applications in the oil and gas, chemical, petrochemical, energy, offshore and steel industries.

Speak to a BM Engineering adviser today for more information about double block and bleed systems by calling 0141 762 0657 or email sales@bmengineering.co.uk.

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