LPG Gas system 1

[Resercher]

I have the following situation:
There are 3 LPG Gas Tanks 2000 Liters (530 Gallons) each supplying a restaurant in a big Housing complex. There is an external underground valve box right outside the restaurant, before going inside the building, having the following valves etc.

1)Solenoid Valve with 2 ball valves together with a by-pass ball valve . The solenoid valve will close under these 4 cases
a)in case of fire (signal from fire alarm panel)
b)from gas detector (in case of fire)
c)Emergency panic break glass
d)in case of low pressure from the tanks.

2)2nd Stage regulator to reduce from 20 psi down to 0.5 psi before going into the building.

3)Low pressure switch whose purpose is to give a signal to the solenoid valve (through the control panel) to shut down in case of low pressure in the tanks.

QUESTIONS:

1) Is this low pressure switch required? Or is it just a waste of money?

2) I could not find this low pressure switch here in the local market so I looked on the Internet. I found so many different items that I got confused. I found a sensor, a transducer and a switch. Which of these do I need? On top of that I had to select between an absolute and a differential type pressure. I would guess that the absolute type is the one that I am looking for.

3) Does the external valve box cover have to be water tight?

I would greately appreciate it is somebody can help on this

 

[Montemayor]

Resercher:

From a safety analysis point of view, a low pressure in the LPG tank indicates one (or both) of two things:

1) You are consuming more vapor from the tanks than can be generated by ambient heat transfer from the atmosphere to the LPG liquid; this is somewhat probable if you are consuming more vapor than can be made up - especially during the winter months.
2) You are running low on LPG liquid content in the tank(s).

The safety consequences of the above points is that your restaurant's oven and stove(s) will shut down for lack of fuel. I think the safety involved has more to do with the restaurant's cash flow than it has to do with a hazardous condition. I've run a lot of LPG supply systems and I've never used a low pressure pressure switch; what I've done to monitor fuel inventory is employ a good level detector/transmitter. Are you outfitted to do something about the low pressure - like activate a vaporizer operation to bring up the vapor pressure in the tank? If you are not at the North Pole, I wouldn't use the low pressure switch. I don't see any useful results from its operation.