WEF Discussion Forums
Operation and Maintenance
Lost of pressure
Hi, we have two 7 hp booster pumps afix with a pressure switch on the line set at out at 60 psi and in at 25 psi. The distribution line is a 1 1/" galvernized pipe running 9 ft up, 5 ft across then down again 10 feet. It then run under ground at a gentle grade to distribute to a 2 level building about 400 feet away. The water is feed from a 10,000 gall vertical tank on the same level as the booster pump located 4 feet away.
The situation is that when we start the pump its not cutting out, but running continuously with pressure at 70psi. However, when we shut down the pump the pressure falls instantly to 20 psi then gradually fall. We put a ball valve on the line at the top about 13 ft away from the pump try again and bleed air from the line and the same thing happen. We even used a different pump, 5 hp, this time the pressure went up to 40 psi run continiously, when shut down the pressure drops to 0 psi.
What is the reason(s) for this and how can we fit this problem? You guys assistance would be greatly appreciated.
Sounds like the same problem we had with our pressure tank, if it is set up the same as ours the Electrode in the Tank is in need of removal and cleaning (on the top of the tank). Your tank sounds like it is full to near the top of the tank, Thus explaining the Pressure dropping so quickly in the Tank. Does your tank have a compresser that pressurizes the Tank? If you do decide to work on the top where the electrode is be sure to lock and tag all sources (Z.E.S.T.) zero energy state training is required for Maintenance work. We removed our tank and feed directly to the discharge line, the tank was checked by a licenced pressure vessel technician and found to be in need of replacement.
Well its not the pressure tank because we removed it from the line in trying to eliminate the possible causes as you mentioned, the pressure is just disappearing from the line in the short span of pipe as soon as the pump is shut off although we lock the line, its just gone without any sign of water or air leak.
The only thing I can think of is check valve? Is it possible the water is flowing back through the pump when it's shut off!
Well we have a lock off behind the pump as well and when we lock it after shutting down the pump nothing change.
The water is going somewhere, do you have access to the Original Drawings? My last guess now is ruptured underground line or the water is being used up elsewhere in the plant due to pressure relief failed or something that will cause a demand for the water. Our 5 H.P. armstrong runs around 50 p.s.i. with-out the Tank and runs continuously feeding the Chlorinator(just the Chlorinator) it also has to pump approx. 10 ft. up and approx. 200' but our line is plastic. Galvanized piping is not the greatest for under-ground and any fittings that are not compatable cause electrolysis and cause the line to plug up and or corrode and break.
regards, D. Maki
The thing is that we can see all the pipe work which is within the building. So there is zero water leak
Put the Tank back in line drain it completely first, make sure the tank is not water logged by this I mean make sure the Tank has an air cushion of about half the tank to 1/4, some tanks have a bladder to provide the air space required and the bladder is pressurized to a couple more p.s.i. than the pump start pressure point and a site glass indicating the water level in the tank. If the tank is full of water the pump will not cylce as it will not reach the pressure to turn the pumps off or will start and stop excessively with very little down time. The feed lines to and from the tank are usually located near the bottom of the tank. If the pump is not capable of reaching the pump stop pressure point it will not reach the pressure switch cut off point, in this case the pressure switch shut off point has to be lowered. every 27" of water in the tank is equal to 1 p.s.i. so if the pressure switch is in the wrong location the pressure gauges will not account for this extra pressure at the pump discharge. My guess is that the pumps cannot pump any more than about 60 p.s.i. our 5 h.p. centrifugal pump will only reach
about 60 p.s.i. max. and thats at 3,500 r.p.m.