Integral Valve InterlocksApplication Data Sheet

Pressure relief safety valve

In many petro-chemical and chemical plants duplication of process components is used to ensure continuous operation. The aim being to run plants for extended periods of time, years or more, without shutting down.

One of the classic examples of duplication is the use of dual or multiple pressure relief safety valves (PSVs) on process vessels and tanks to ensure safety of operation. An additional requirement of having dual PSVs is that one or more relief valves must always be in service to maintain safety.

There are several ways of ensuring that a PSV is always in service, the simplest being to use standard manual block valves fitted with key operated valve interlocks. The Kirk range of Eagle Valve Interlocks can be supplied to mount directly on to the system block valves with the locks keyed to maintain the operational requirements of a relief valve system.

Quarter-Turn or Multi-Turn valve interlocks being used dependent on the type of valve which they are controlling – Quarter-Turn for ball, plug or butterfly valves or Mutli-Turn for gate, globe or gearbox operated valves.

Please see overleaf for details of operation of a typical dual PSV system. Other key logics can be supplied for multiple PSVs.

www.Kirkkey.comProcess safety Control

Indu

stri

esOil Refinery

Petro-Chemical

Pulp & Paper

Liquefied Gases

Food Bulk Handling

Multi-Turn Valve Interlock

Quarter-Turn Valve Interlock

INITIAL SYSTEM STATUS: PSV “B” is in service and PSV “A” is isolated for maintenance. Valves 1 & 2 are locked closed, valves 3 & 4 are locked open. Key A is held under Supervisory Control.

SYSTEM OPERATION: 1) Key A is issued to an operator from

the Supervisor in the Control Room together with a Permit to Work (PtW)

2) The operator enters Key A into the lock fitted to Valve 1, to unlock and allow the valve to be opened. Key B is removed from the lock to lock the valve open.

3) The operator enters Key B into the lock fitted to Valve 2, to unlock and allow the valve to be opened. Key C is removed from the lock to lock the valve open.

4) The operator enters Key C into the lock fitted to Valve 3, to unlock and allow the valve to be closed. Key D is removed from the lock to lock the valve closed.

5) The operator enters Key D into the lock fitted to Valve 4, to unlock and allow the valve to be closed. Key E is removed from the lock to lock the valve closed.

6) Key E is returned to the Supervisor in the Control Room to signify the operation has been completed.

7) PSV “A” is now in service and PSV “B” is isolated for maintenance.

8) The sequence can be reversed to return to the initial system status.

Interlocking Logic

Operation

Integral Valve interlocksApplication Data Sheet

Interlocking designs can be made to suit any operational Requirements

www.Kirkkey.com

Pressure Relief Safety Valve

The interlocking logic shown illustrates a typical operational sequence for a dual pressure relief system.

D E

CD B

C

A B

E

A

Supervisory Control

Valve 3LockedOpen

Valve 2LockedClosed

Valve 4LockedOpen

Valve 1LockedClosed

Pressure Vessel

To Flare

PSV “A”In Service

PSV “B”In Service

PSV “B”Isolated

PSV “A”Isolated

In ServiceKey Held Isolated

Key A

Key B

Key C

Key D

PSV “B”

PSV “A”

Key E

LegendDual Key Valve Locked Open

Dual Key Valve Locked Closed

Key Free Key Trapped

STEP

1

2

3

4

A

B

C

B

A B C

B

C

B

A

KEYIN

KEYOUT

SequenceControl Unit

H2 Valve CO2 Valve Air Valve

Operating Knob

STEP

1

2

3

4

A

B

C

B

A B C

B

C

B

A

KEYIN

KEYOUT

SequenceControl Unit

H2 Valve CO2 Valve Air Valve

Operating Knob

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