Convertible Jet Pump Won't Build Pressure

Have a 1/2 HP convertible two pipe jet pump deep well application. 90'. Pressure set for 20-40. Pump won't build pressure past 23 psi and won't push water into bladder tank. 18 psi air pressure in bladder tank without water or water pressure in tank. Pump has trouble priming but eventually does and builds to only 23 psi even with discharge valve on pump closed. If I bleed off air pressure in tank to zero I can get water to flow into tank but still doesn't build water pressure past 23 psi. Ejector and foot valve are new. Water level is ~13' below surface in 6" well casing so I believe I have enough water. Pump has been rebuilt but still won't build pressure. New pump was installed with same result. System seems to hold pressure if I manually shut off pump. No check valves installed between footvalve and pump that would hold in pressure. Would a pin hole leak in suction line cause this or would it have to be bigger? I've pulled the pipes (plastic) from down the well and didn't see any leaks there. Could I be leaking at the well head connections even though I don't see any water or hear any running back down the well? Well head is 50+ year old. Piping is faily new, 10 years. Pipes from well head to pump are underground about 12' run. Does it look like I'm gonna be digging?

You said the pump was rebuilt. What does that mean?

With only 23 lbs, it sounds like a plugged jet, or possibly (since you said it was new) a wrong nozzle and venturi. More than likely though, the jet (nozzle) is plugged with a piece of scale. When you pull it out next time, take the jet off and look into the venturi tube. You should see the nozzle below it and the hole in the nozzle should be clear. Also wash it out in a bucket of water to flush any scale that might be hiding in it. Take a drill set and measure the hole size in the nozzle and venture. They should be in 32nds of an inch or smaller.

You said water is only 13' below surface, a shallow well jet pump would work fine from that level unless your water level fluctuates to below 25 feet.

bob...

When rebuiilt, the impeller and diffusers and o-rings were replaced. Didn't do the seal since it wasn't leaking and the carbon ring looked fine. I got a different pump from a friend and hooked it up with the same result though. The ejector is new and the nozzle and venturi are the same size as the original. I have multiple nozzles and venturi's that came with the ejector and matched it up with the old one. I even put the old nozzle and venturi in the new ejector with the same low pressure result. Both the new and old nozzles have about a 1/4" orifice and the new and old venturi's have about a 3/8" orifice. Parts were ordered through Grainger/Teel with them cross referrencing the model pump and ejector that I had. I had the new ejector apart and it's all clear. What's puzzling is that the low pressure is the same problem I was having even before I rebuilt the pump and replaced the ejector and foot valve so I'm thinking that i'm missing something.

That's a real puzzler. I don't ever expect much with a 1/2hp pump and a two pipe jet, but you should be able to make at least 40 psi. The nozzle and venture sizes sound a little large to me for a 1/2hp to be making much pressure though.

An air leak would keep it from priming or would make it pump very slow depending on how big the leak, so that's not what I think is happening.

You said you replaced the impeller and diffusers "s", is this a two stage pump (two impellers)? What brand is this pump? If it's from Graingers, I'll never know without a picture. They buy from lots of companies then put their name on it.

bob...

It's a single stage (one impeller) 1/2 hp Teel convertible jet pump circa 1993. The parts list when rebuilt listed two parts as "diffuser". One was the actual plastic diffuser that surrounds the impeller the other was a rubber ring that the diffuser mounted to the suction of the pump head with.

I'm still not sure it's the pump since I had the same low pressure symptoms with a different pump in place.

How much difference in pressure would I expect if I put a smaller nozzle and venturi in?

Thanks for your help.

A smaller nozzle and venturi should help increase it's pressure. The second diffuser, the rubber piece. If you didn't get that perfectly in place, you would be experiencing this same sort of problem. You might want to check that it didn't get pinched or pushed off it's seat.

bob...