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PCS and SIS signals acting on a single on/off valve

PCS and SIS signals acting on a single on/off valve

PCS and SIS signals acting on a single on/off valve

(OP)
Hi,

I am working on a project which is in Detail Design/Execution Phase. Part of the new system is a inlet manifold which is equipped with SOV Emergency Shut-Down valves for isolation and safety. The manifold is also equipped with a well testing header and to be able to switch the wells from production to testing the operators will have to manipulate the ESDVs as no other valves were considered in the design apart from the ESOV. For this purpuse the idea came to install a second Solenoid on the Valve with a signal from the PCS, thus having two solenoids on the same valve with signals from two systems SIS and PCS. I would avoid having two sistems acting on the same valve, and I would just add another valve with a signal from the PCS.

I would like to know if somebody has encountered this arrangement (two signals from two different systems on the same valve) and what issues came out of it?

many thaks,
Vlad
Replies continue below

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RE: PCS and SIS signals acting on a single on/off valve

Quote (OP)

(two signals from two different systems on the same valve)
The issue will be codes and failure modes.
The system should be arranged so that the ESDV control overrides the other signal. Consider whether any failure in the PCS system may impact the ESD function. Check your safety codes very carefully to see if using an ESDV for other functions in addition to ESD is allowed.

Quote (OP)

I would like to know if somebody has encountered this arrangement (two signals from two different systems on the same valve) and what issues came out of it?
Yes but not for ESD.
We had a burner on an oil heater. The volume of combustion air was controlled by a an air operated damper. It was desired that the damper be fully open during the purge cycle. We used a three way solenoid valve to interupt the control air from the control instrument and use air from a pressure regulator to force the damper fully open. At the end of the purge cycle control was returned to the control instrument.
I can't recal any problems, but I stress that this system was not a safety system.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: PCS and SIS signals acting on a single on/off valve

Quote (waross)

oil heater <snip> combustion air <snip> damper be fully open during the purge cycle

Quote (waross)

this system was not a safety system

Actually, it is a safety system. The pre-ignition purge is one sequential function in a combustion flame safety system light off:

NFPA 86
8.4.1.2 A timed preignition purge shall be provided.
(C) To begin the timed preignition purge interval, both of the following conditions shall be satisfied:
(1) The minimum required preignition airflow is proved.
(2) The safety shutoff valve(s) is proved closed.

If the combustion air damper does not open, whatever sensor proves the purge airflow should interlock the flame safety controller in absence of sufficient purge air flow.

RE: PCS and SIS signals acting on a single on/off valve

I guess I should have said a safety shut down system. It was a long time ago and I don't remember all the details but the circuit met the codes in place at that time and place.
My main point was that complying with the codes in effect will be the most important.
I think that your information supports that point, Dan.
Thanks.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: PCS and SIS signals acting on a single on/off valve

We often have valves controlled from a DCS with an interlock solenoid fed from the ESD system.
We sometimes have an ON/Off valve with two solenoids one from the DCS the other from the ESD
It's also possible to have a valve interlocked to the EDS while it has a request from the DCS to open/close it, the ESD of course takes precedence.
Transmitters can be wired to both systems also but must be wired in such a way that if the wires fall off the DCS the signal will still get to the ESD

RE: PCS and SIS signals acting on a single on/off valve

(OP)
i know it comes a couple of months late, but I forgot to say thank you, I apologize for that.

cheers,
vlad

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