slow pump and pressure drops to near zero when it kicks in

[Arundel]

It's a submersible 3/4hp Franklin pump, but I do not know the well depth. The amp reading on two wires, black and yellow, are a steady 5.7 amps when the pump runs. The 30/60 pressure tank, ~20 gallons, takes 4 or 5 minutes to fill. When opening taps, the switch kicks on at about 25 lbs and instantly the pressure gauge goes to near zero and I can stop the flow with my finger for about 20 seconds until
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pressure begins to build. What's going on?

 

[RS]

We had a similar situation when we bought our current home, and all I had to do was lower the preload in the pressure tank. If the pressure tank came preloaded for a 40-60 pressure switch setting, but the pump isn't starting until 25, that may be your problem. If the switch is set to 40-60, the tank should be preloaded to38. Not all gauges are accurate, so you have to adjust either the switch or the preload until it works properly. The way I test a system is to shut off the power to the pump, then slowly bleed off the water. When the switch clicks, the gauge should slowly drop another 2 psi, then quickly drop to 0. Our original pressure tank failed prematurely, and I suspect it happened because it wasn't set up properly, luckily it was under warranty.

 

[Arundel]

We had a similar situation when we bought our current home, and all I had to do was lower the preload in the pressure tank. If the pressure tank came preloaded for a 40-60 pressure switch setting, but the pump isn't starting until 25, that may be your problem. If the switch is set to 40-60, the tank should be preloaded to38. Not all gauges are accurate, so you have to adjust either the switch or the preload until it works properly. The way I test a system is to shut off the power to the pump, then slowly bleed off the water. When the switch clicks, the gauge should slowly drop another 2 psi, then quickly drop to 0. Our original pressure tank failed prematurely, and I suspect it happened because it wasn't set up properly, luckily it was under warranty.

Your clear observation sounds right, thx. I'll pursue the tank pressure / pressure switch marriage. The tank is preloaded to 28 (the spec on the tank; 22 years old) but the p switch is cutting out at 60 and cutting in at 25. What confuses me is why the pressure disappears when the pump kicks in. Where does it go? Check valve at the pump? Anyway I'll pursue the pressure switch adjustment first.

 

[GReynolds929]

Because the tank pressure is higher than the cut in pressure so the tank loses all pressure before the pump kicks on. This is why the tank pressure should be 2-5 psi lower than the cut in pressure.

 

[Arundel]

Because the tank pressure is higher than the cut in pressure so the tank loses all pressure before the pump kicks on. This is why the tank pressure should be 2-5 psi lower than the cut in pressure.

Thx ! I think this is part of it. I adjusted the cut in/out pressure to many points. Every adjustment produced a predictable high cut off (up 70 at one point), but the low remained at just about 30 (tank pressure reduced to 27). Next I'll try swapping out the pressure switch. I wondered whether the capacitor in the start control box could cause this odd drop in pressure when the pump kicked in; ie starting backwards? The capacitor tested 118; the spec is 86 - 103. Is that significant?

 

[RS]

I really don't think you need to change the pressure switch, but maybe clean the points. Watch the points when they snap shut, there shouldn't be any arcing. It's possible the little pipe leading from the manifold to the pressure switch is plugged, or even the area under the diaphragm in the switch has a buildup pf scale. You would need to disconnect the wires to remove the switch, so for < $20 You might want to install a new one. Is you water high in calcium or iron, do you get scale build up? I don't think it's possible for the pump to start backwards, but I am unsure about the capacitor, hopefully someone more knowledgeable will comment. I have changed one that was bad, but it was over 40 years ago.

 

[Valveman]

The air charge in the tank does need to be less than pump start pressure or you will see a quick hesitation of flow. But taking that long to put 5 gallons in a 20 gallon size tank is not right. 5.7 amps means the pump is putting out max flow. So, I suspect a hole in the drop pipe just above the pump. Are you seeing any air in the faucets?

You can remove or gut that check valve just left of the tank tee to see if you have a leak down hole.

 

[Arundel]

The air charge in the tank does need to be less than pump start pressure or you will see a quick hesitation of flow. But taking that long to put 5 gallons in a 20 gallon size tank is not right. 5.7 amps means the pump is putting out max flow. So, I suspect a hole in the drop pipe just above the pump. Are you seeing any air in the faucets?

You can remove or gut that check valve just left of the tank tee to see if you have a leak down hole.

Thx Valveman. By now we’re convinced that something is wonky down the well, but I like your suggestion to remove the check valve at the pressure tank as another diagnosis. Need to find a heavy duty lift. It appears to be galvanized pipe below the pitless adapter.

 

[Valveman]

With the flexible hose it will be easy to remove or gut that check valve.