6ö MOV and gate valve fitting to fitting.

[Kajtek08]

I have a client who wants to install a 6” MOV and a gate valve fitting to fitting on a gasoline storage tank suction line. Is that could practice? Should there be a spool in between with a drain so when the tank is isolated (gate valve) the spool could be drained and the MOV could be replaced/repaired if required?

 

[BigInch]

What happens if the gate valve needs to be repaired. The number of valves in the line doesn't matter. If the wrong one fails, you still need to drain the tank.

An open/close MOV won't require any more maintenance on fluid containing parts than any other valve and the Motor can be repaired without draining the tank.

Independent events are seldomly independent.

 

[LittleInch]

The thing that would concern me is thermal expansion of the gasoline between two closed valves if closed on a cool day, but subject to heating could develop really quite high pressures. Whilst the volumes may be small and only need a small amount to leak, you can damage valve seats due to this and gasoline is one of the higher thermal expansion liquid hydrocarbons.

A spool is often useful to provide a support for these quite weighty valves and avoid propping the valve body itself. You can then also put in a thermal relief line draining into a drain or back into the tank.

Otherwise I agree with BI, the fact you're bolted to the isolation should make no difference as to whether you can take the MOV off. All yuo would need to do is hve a small drain pot when you crack the bolts - not too clever, but you're only doing this every few years. A spool would be better but you could find your drain valve seized closed due to inaction....

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way