Pilot-Operated Relief Valve

Safe is a relative term

Example: Upon declaring emergency and deciding to return to airfield, airliner must first dump fuel. Thousands of pounds of fuel is now sprayed out of the tanks to the atmosphere.

It is not environmentally friendly, it is only mostly safe; but it is essential to the safety of those on board during landing - so it is accepted.

One of the options is to substitute the toxic material with a safer material.

We know what the words say, but alas, we have no idea what you mean.

milo

In valves the "pilot" is not the same as in a plane!

Pilot operated valves are 2 stages valves for -usually- big flows and which for reasons of sensitivity are designed as a differential piston with an area on the closing side > than the one on the opening side. As long as the "pilot" which is a simple spring loaded relief valve does not reach the opening threshold the pressure force on the closing side > the force on the opening side since pressure is same on both sides. Between the 2 surfaces of the main piston an orifice takes care of this equalisation. If the "pilot" stage opens then the pressure on the closing side drops and the flow is limited by the orifice (mentioned above). The Force on the opening side becomes bigger than the other and the main valve opens. If the pressure on the "pilot" goes down, the via the orifice the chamber is again filled with fluid and due to this the main valve closes.

I think Milo was the only one to be honest and say he does not understand the main request. I unfortunately noticed very often that answers are not on target an that's a pity for the renomee of CR4.

"The most accurate design is the pilot-operated relief valve. As you would expect,
it is also the most complex, and expensive. The pilot relief valve is really made up
by using two valves. The pilot senses the pressure to be relieved, and loads or
unloads the main relief valve. This design minimizes the amount of pressure
buildup over the setpoint that is required to provide the required capacity. They
do have large relief capacity and are available in larger sizes than other types of
reliefs."

Not possible to answer the OP's question definitively as he does not give details of the valve make, product etc. The pilot valve usually has an exhaust which can be led to the flare system or to safe location. The back pressure of the flare system must be taken into account or a bellows type pilot fitted.

All connections.......inlet, outlet, discharge,drain and valve spindle have seals, and obviously should not leak.

Why would it leak, unless a seal is faulty..........or incorrect seals have been fitted, e.g. for the type of fluid............and we can say the same with any piece of equipment............if a seal, union, pipe weld etc., is faulty or incorrect.........it will leak. It doesn't care whether or not it is a toxic fluid, or whatever.

"If its broke fix it."..........or as many do today, replace it.

I think I know what Heita is talking about. Some of these pilot valves have a weep hole in the spring housing in the event that the o-rings on the pilot valve stem (or sleeve) fail and the fluid enters the spring housing thus potentially affecting the spring setting and even worse cause overpressurisation and catastrophic failure of the spring housing.

You can only tube from the pilot valve to a safe location if the pilot valve housing and weep hole outlet is pressure rated (in most cases its not). I've noted that vendors don't really advertise this weep hole (funny that!). You won't see it on their drawings but try the troubleshooting section!

Cheers

Mozzie