New phenomena of Pr.drop in fire water network

[nesamani05]

We are in one LPG pumping station of cross country LPG pipeline system.
We have fire water network ( length of the pipeline is < 2 km). Water is pressurised(8.5 Kg/cm2) by 2(1+1) Jockey pump(15 m3/hr, 88 m) & 2 DEG pumps(410 m3/hr & 88m). Set point for Jockey is, starts at 7.5 and stops at 8.5 kg/cm2. Nowadays we are observing one different phenomena, During day time (from 8 am to 6 pm) water pr is more than 8.5 kg/cm2, used to be 11 kg/cm2. from 6 pm to 8 am , pr drops from 8.5 to 7.5 within 40 min. so jockey starts for every 40 min to maintain the pr.
Why this is happening...?
how to prevent jockey frequently running...?

 

[BigInch]

That would normally be associated with the Sun going down and the pipe beginning to radiate heat away with additonal convective cooling from lower air temperatures during the evening. Is the 40 minutes happening just before, during and after sunset? I think so.

We are more connected to everyone in the world than we've ever been before, except to the person sitting next to us. Lisa Gansky

 

[BigInch]

At the rate things are going around there, you probably have another small leak in the system which is making the sundown effects noticable now.

We are more connected to everyone in the world than we've ever been before, except to the person sitting next to us. Lisa Gansky