Solenoid valve at series.

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srinivasan

srinivasan

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I am going through the specification of International marine std for incinerator [MEPC 76(40)] where it is mentioned "Two fuel control solenoid valves should be provided in series in the fuel supply line to each burner". Here i got doubt. If Solenoid valves are Normally closed type (Failed close-usually for fuel control operation) and one valve failed, other valve also will not do any work. If two valves are in parallel, this will be considered as redundancy valve but in series... Can anybody clarify, purpose of connecting two valves in series.
 
IMO the reference is to connecting the valves in series in the fuel line so either can shut fuel off. Not electrically in series. That way if one valve fails mechanically in the open position (e.g. from corrosion or debris in the fuel) the other valve can still cut off the flow.
The alternative (not to be used) is to put two valves in parallel to get twice the flow rate from valves which are too small.

Tapatalk!
 
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In the entertainment and special effects world, fuel valves are PLUMBED in series to ensure that a blocked / sticky / failed valve will not cause a situation where fuel cannot be shut off.

Valves are sometimes WIRED in parallel so that they are actuated by the same circuit. Other times, valves are wired to separate actuation circuits, so that the failure of a single channel of a safety circuit (welded relay contacts, for instance) to interrupt power to the valve will not cause a situation where fuel cannot be shut off.

I imagine a similar control and safing methodology would exist in other industries as well.

SceneryDriver
 
GoldDigger said:
IMO the reference is to connecting the valves in series in the fuel line so either can shut fuel off. Not electrically in series. That way if one valve fails mechanically in the open position (e.g. from corrosion or debris in the fuel) the other valve can still cut off the flow.
The alternative (not to be used) is to put two valves in parallel to get twice the flow rate from valves which are too small.

Tapatalk!
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Thank you for all the answers. In simple, one valve (Normally closed) is enough to cut off the flow but for mechanical failure, more than one is need. Here another query, If one valve is failed electrically (will be in closed position after failed but no feedback in design), burner will not get fuel. so burner will give the fault feedback to control system and we can analyse the causes. but any easy method is there to find which valve is failed out off two without removing from pipeline.
 
You can tell whether each valve is getting the actuation voltage with a meter but I do not know of any simple way to tell if a valve is stuck closed without removing it or bypassing the other valve.
If the controls try to close both valves when no flame is defected, you have even less info to work with after the fact.
I suppose you could design the system with multiple pressure sensors, but that is not going to help you in s system without them.

Tapatalk!
 
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srinivasan said:
... but any easy method is there to find which valve is failed out off two without removing from pipeline.
Click to expand...
Provide 3 low gas pressure switches, one upstream of the two valves, one between the two valves, and one downstream of the two valves. I have seen this arrangement on industrial gas fired boilers.
 
Most any higher capacity burner I have ever seen always has two gas valves in series. The idea from a fire safety point of view is that you need some assurance that if one valve fails to close when it is supposed to the other one hopefully does close.

If you don't have any monitoring of performance though it is a little pointless - if one valve should fail it will still operate with no apparent problems until the second valve fails to close. By using the three mentioned pressure switches one can tell the combustion controller things are in the proper state before it will allow proceeding with operations, and this is sometimes in the pre-purge or at least before ignition part of the combustion control program cycle and needs to be proven before the program will move to the next step.
 
Residential gas dryers have two solenoid valves in series, built into one body with three coils (two on one of the valve sections). The way it is built, either one failing will prevent the device from working, and they are part of the flame assurance system. Real clever design.
 
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