Whats the difference between Liquid Expansion Valve F.S.D and Thermostat?

[plumbing1981]

Hello

What is the difference between a Liquid Expansion Valve (Flame Supervision Device) and a Liquid Expansion Valve Thermostat. They both seem to have all the same parts inc. tempreture sensing bulb, bellows, closing spring etc and both control the gas flow to the burner and have a bypass. So why does the cooker need both devices when they seem to do the same thing?

 

[quality]

In a few words the FSD is controlled by the temp at the sensing phial opposed the pressure supplied to the burner , the thermostat has a similar temperature sensing method which acts direct

 

[Puddle]

Well if you know my wife’s cooking you would realise that as many controls on the cooker as possible is a good thing
But having said that
Firstly one is a safety devise and the other is a control so even if they did the same thing ,no safety devise should be used in the standard operation of an appliance

And probe positions would have to be in different locations anyway

But in this case there actions are opposites


A FSD will start life in a closed position, keeping a flame low, through it’s pass, until probe(set across low flame) becomes hot then will open fully, allowing gas to pass freely ,no heat,no open

A thermostat will start life in the fully open position when oven cold and as probe heated(usually in top ,back of oven) will start to restrict and close down gas flow,no heat,no close


Also it is a requirement of the cooker thermostat to be able to be adjusted to the temp required ,this would not be allowed for a safety devise



imho

 

[plumbing1981]

Thats has cleared things up cheers