ARV sizing for firewater system on Offshore platform
ARV sizing for firewater system on Offshore platform
(OP)
Hi all,
Im currently doing a transient analysis pressure surge for firewater system. I have problem in sizing the right Air Release Valve at the highest point of the system.
Comparing 2 cases,
Case 1
when the deluge valve for the largest fire zone is opened, there are large amount of water (1800 m3/hr) will flow out from the system thus creating a vacuum at the highest point. Ive then put the ARV at some point and the surge (due to vacuum formation) is solved. The ARV size is 4"x4" with the orifice size of 6/64" (2.34mm)
Case 2
when two firewater monitors at the helideck are activated, the amount of water flowing out the system is much smaller (270 m3/hr) compare to case 1. By using the same ARV size and location (supposed to), there is high pressure surge happened at the ARV section.
After i change the ARV size from 4"x4" to 1"x1", the surge problem is gone.
So, it looks like Case 1 needs a large ARV and Case 2 needs a small ARV. and there is no size in between is suitable.
Can anybody in here know why is this happening and how to solve it? Really appreciate if you guys can help me. thank you in advance.
Regards,
Fikree
Im currently doing a transient analysis pressure surge for firewater system. I have problem in sizing the right Air Release Valve at the highest point of the system.
Comparing 2 cases,
Case 1
when the deluge valve for the largest fire zone is opened, there are large amount of water (1800 m3/hr) will flow out from the system thus creating a vacuum at the highest point. Ive then put the ARV at some point and the surge (due to vacuum formation) is solved. The ARV size is 4"x4" with the orifice size of 6/64" (2.34mm)
Case 2
when two firewater monitors at the helideck are activated, the amount of water flowing out the system is much smaller (270 m3/hr) compare to case 1. By using the same ARV size and location (supposed to), there is high pressure surge happened at the ARV section.
After i change the ARV size from 4"x4" to 1"x1", the surge problem is gone.
So, it looks like Case 1 needs a large ARV and Case 2 needs a small ARV. and there is no size in between is suitable.
Can anybody in here know why is this happening and how to solve it? Really appreciate if you guys can help me. thank you in advance.
Regards,
Fikree





RE: ARV sizing for firewater system on Offshore platform
My focus: Alloy Valves Super Duplex Valves Monel Valves Incoloy Valves Titanium Valves Hastelloy Valves
RE: ARV sizing for firewater system on Offshore platform
Thanks.
RE: ARV sizing for firewater system on Offshore platform
"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.
http://waterhammer.hopout.com.au/
RE: ARV sizing for firewater system on Offshore platform
in normal pipe line application, the water is actually in a motion and the vacuum is form due to sudden stopping of the pump. In the case of fire water system, the water in the pipe is in standstill before the deluge valve and the monitors are open. You will not get such a high flow rate instantly.The initial stored pressure in the fire main will not be able to provide you the designed flow rate. Full flow will only be achieved with the main fire pump in full speed.
RE: ARV sizing for firewater system on Offshore platform
Either way the real physics is the simple art of balancing input and output of water and maintaining the pressure in the line sufficiently high (through the pumps) to give the correct amount out of the given (or calculated) openings (deluge valves) without creating water hammer when filling and/or vacuum collapse if sudden vacuum should occur.
Excessive air relief out of the pipeline is only necessary if the pipelines are empty (filled with air) when you start to fill the system at full firefighting capacity (eg more than normal air relief at normal filling speed).
In any case: this is the simple way of calculating water in equals air out (opposite if vacuum). Air out of orifice should have a reasonable speeed comparable to normal speed of for instance steam/gas in pipelines (say 30 o 50m/s) and in addition the air relief valve/system must be equipped with damping, not to create waterhammer when the system is filled with water and water pressure builds up.
One valve of this type should be sufficient for both capacities.
Your orifices seems small if the above is the case.
Or have I misunderstood your problem or the physics?
RE: ARV sizing for firewater system on Offshore platform
"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.
http://waterhammer.hopout.com.au/