Continuous Operation of Fire-Booster Pump

You have to go through following check list to sort out the problem: 1). Generally, you find head in meter unit on pump name plate rather than pressure unit. Kindly check this again & also, confirm with supplier. 2). Check shutoff pressure of pump. If it is showing 160 psi pressure, then pump functioning is okay. 3). Have you taken the jockey pump for maintenance before the starting of problem? If yes, clearance between back plate & impeller is to be checked. 4). Ensure that suction line is clear (from debris, choking of strainer etc). 5). Calibrate pressure guage & pressure switch to avoid deviation in pressure difference. 6). If all above points are okay then there must be some leakages in underground piping. You have not mentioned the tapping location of pressure guage whether after pump discharge NRV or before pump discharge NRV, pressure fluctuates or not, which would give more clarity to provide solution.

'' 2). Check shutoff pressure of pump. If it is showing 160 psi pressure, then pump functioning is okay.''

My understanding is rated pressure 160 psi (375 feet) is the pressure at which the pump should operate when the discharge valve is fully open and not the shutoff head.

'' 6). If all above points are okay then there must be some leakages in underground piping.''

all the other issues related to pump and system is fine except that we suspect there are leakages and unauthorised fire water usage. then does stopping the leakages will raise the main header pressure and why the pump is operating at head below its rated head?

If a 160 psi pump is only putting out 100 psi, it's worn out, needs a rebuild.

It would be nice if you could detect flow somehow, that would answer a lot of questions, especially about any mystery flow.

You're saying the main header pressure cannot go above 120 psi, but want the jockey pump to cut in at 140 psi, that does not compute.

Centrifugal pumps are not all that great at making pressure without flow, is this a positive displacement pump? Is there a pressure tank in the system?

Yeah. Either that or there's a leak! <Chuckle, wheeze, splutter>

Two issues-

First- You say the pump is RATED for 160 PSIG but what is the rated head of the pump and what is the pressure of the inlet water that is being boosted. A pump rated for 160 PSIG but with a 200 Foot (~80 PSIG) boost and a 40 PSIG inlet will never make 140 PSIG or higher for switch shut-off.

Second- IF the pump dynamic boost rating AND the inlet pressure will allow over 140 PSIG net discharge, is the pump a 3-phase pump that is wired "backwards" and spinning the wrong way? A quick shut-down while looking at the pump windings will tell you.

If you do not have a system leak, the jockey pump either needs replacing, or if you are technically competent, rebuilding.

Already good suggestion given,one more is to check if there is a Hydrant in the Fire line open or leaking badly?or a ruptured fire line in the discharge system.