7 replies to this topic

[R NESAMANI]

Dear All, I am in one pumping station of LPG cross country P/L system.
We have a pressure drop in fire water network, which is to be maintained at 8 kg/cm2.
Jockey is to start at 7 kg/cm2 and stop at 8 kg/cm2.
Because of the pressure drop, jockey runs for every 30 mins(approx) only in night time.
During day time, FW network pr goes upto 14 kg/cm2.(Due to evaporation of water,may be).

Why this is happening...? How to pinpoint the problem?

[ankur2061]

Nesamani,

Please note that if you are using above ground firewater network you need to coat your above ground fire water piping with a refelctive coating so that it absorbs very little heat from solar radiation. This also one of the reasons that most of the firewater network found in the middle east is buried due to the extremely high daytime solar radiation.

However, if your firewater piping is designed for the black bulb temperature (85 deg C used in the middle east) and for the main fire water pump shut-off head then I do not foresee any problem.

Regards,
Ankur.

[kkala]

Black bulb temperature (http://engineers.ihs...DXJIBAAAAAAAAAA is quite useful. In Greece (not far from middle east) piping design temperature due to solar radiation is considered as 70 oC (according to a practice), it may have to increase a bit.
The jockey pump replaces the leakages from fire water network, restoring its pressure to 8 kg/cm2 (g?) during night. One would expect more or less same leakages in the day, but these do not occur. Pressure increase to 14 kg/cm2 can be attributed to thermal liquid expansion in an isolated system, but (as far as I have heard and can suppose) a fire water network has some leakages always.
So I would check (α) whether observed pressure of 14 kg/cm2 concerns the whole fire water network or a short part of it, well isolated. (β) whether fire water is taken at night for some use not practiced in the day. It is not easy to find it out in a big factory.
Note: Over here fire water is sometimes used for washing, even though this is discouraged.

Edited by kkala, 02 October 2011 - 01:38 PM.

[breizh]

You may have safety valves leaking on your system ( I already experienced this ) or operators doing some cleaning activity at night!

Breizh

Edited by breizh, 02 October 2011 - 07:54 PM.

[R NESAMANI]

Thank you all for your reply.

-->Kkala ---> Total network length is less than 1.5 km. In that also, buried P/L length is 300 mtr. So how to approach the leakage problem.

-->Breizh --->Can you explain the safety valves leaking problem.

[breizh]

I don't remember the excact issue except that the Psv at the discharge of the pumps were not working properly ( Setting ?).

Breizh

[fraz rizvi]

Hello,

I think this may be due to the thermal expansion of liquid during the day time and I suggest you to have a PCV on your fire water network; discharging back to the fire water tank; just in case your piping is not designed for black bulb temperature.


Fraz RIzvi

[kkala]

-->Kkala ---> Total network length is less than 1.5 km. In that also, buried P/L length is 300 mtr. So how to approach the leakage problem.

Taking the local situation as an example, it is not easy to suppose that the whole network of 1.5 km does not have leakages. I would stop/isolate jockey pumps in the morning, with the discharge pressure P at 7-8 Barg. Then I would follow the increase of P with time, being sure by observation that only valves at network exit are closed, no jockey or other pump operates intermittently, no leakages are detected. Pipe of 1.5 km can be easily supervised, by (say) two persons. If no reason of pressure increase is detected, then it may due to thermal expansion and proper measures may be necessary. You can see if pressure is reduced by opening an exit valve for (say) a few seconds.
Even if no leakages are detected, check valves at the discharge of the pumps could leave some backflow to fire water tank. I have not heard of pressure increase in fire water network here, where local conditions in summer may not be far different to middle east.

Edited by kkala, 11 November 2011 - 02:56 PM.