LPG Gas 2

[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 perpose 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

 

[TBP]

What does the fuel utilization code for your jurisdiction call for? That would be the place to start.

 

[Resercher]

I am Working here in Riyadh, Saudi Arabia. I do not think they have any code here. Even if they have one it would be no good to me, since everything is in Arabic

 

[hydrae]

The shut down on low pressure in the tanks is to prevent oxygen or air from entering the tanks,
If there is air in the tanks it needs to be purged prior to refilling, a process the gas supplier normally does. purging can be done by pulling vacuum or by repeated low level filling and venting, either case it cost time, money and gas.

The purging is for safety reasons and to provide a consistant flow of gas to the fixtures

Hydrae

 

[Drazen]

For this purpose it appears you need switch, not sensor/transducer (which are used in process control).

If I undestood you well, your valve box is mounted underground, normaly it should be watertight, but assuming that there is no any underground water in Saudi Arabia, it seems you can omit it. (What kind of surface protection is used for tanks - if they are installed under ground as well? That should give some clue.)

 

[Resercher]

Mr. Hydrae, how can oxygen or air enter into the system if both the piping and the tank are air-tight? If the gas tanks were not air tight then all the gas would leak out.

 

[kbs]

Resercher

NFPA 54 states
"5.11 Low Pressure Protection. A protective device shall be installed between the meter and the appliance if the operation of the appliance is such (i.e., a gas compressor)that it could produce a vacuum or a dangerous reduction in gas pressure at the meter; such devices include, but are not limited to, mechanical, diaphragm operated, or electrically operated low pressure shutoff valves."

You should always install these devices on underground propane delivery lines as you can never tell if the restaurant isn't going to move and another business moves in with a vacuum-developing appliance. Safety first.

Your propane delivery company should be able to source one for you.

 

[hydrae]

Mr Resercher

When the tanks are empty and the stove is on, the hole where the gas leaks out is a source where air can leak in.

Temperature variations with complex piping can create vacuums in some areas
Engine driven generators also produce vacuum during operation or starting, a dual fuel application also follows the complex piping scheme.

Mr Hydrae