0psi air precharge in bladder tank?

[Johnnyh55]

this week the hose from my shallow well jet pumpto my bladder tank burst and as I was replacing it and the bladder tank was empty of water i took an air pressure reading and my car tester read 0 psi. i replaced the hose and everything is working like it was before but I don't think it's normal to have 0psi precharge. it even says on the tank, factory precharge at 28psi. what could happen if I leave it this way and what would be the benefits of adding some air? i took a reading when the tank water pressure was at 55psi and the air pressure read 50psi. my pressure switch is set for cut in at 48psi and cut out at 68psi

 

[Reach4]

Your tank is is very probably bad.

On the new one, set the air precharge to 44 or 45 PSI.

You could try putting 44 or 45 psi of air into the old one (with water pressure=0), but it will probably not last. It could hold you for a few days while you shop for the new tank. Or just add some air, and it would give you a little temporary relief.

The new tank should make the pump take a minute or more to shut off. 30 seconds is not terrible, but not good.

 

[Sponsor]

 

[LLigetfa]

i took a reading when the tank water pressure was at 55psi and the air pressure read 50psi.

One or both of your gauges are reading wrong. You need to know which is right and compensate for the bad reading. Precharge on a jet pump system should be 5 PSI less than cut-in.

 

[Reach4]

One or both of your gauges are reading wrong. You need to know which is right and compensate for the bad reading. Precharge on a jet pump system should be 5 PSI less than cut-in.

One thing... if the precharge is a little high, it does not damage the tank. What having a little too much precharge air does is to cause a stutter in the flow as the pump cuts on.

I have never used a jet pump, but I expect there might be more variation in response time vs submersibles.

 

[LLigetfa]

A jet pump uses pressure to make more pressure so the "stutter" can be quite pronounced. If the pressure switch has a low pressure cutoff, it can also bounce the switch causing it to arc and fuse or trip it requiring human intervention. A little too much is worse than a little too little is.

 

[Reach4]

If the pressure switch has a low pressure cutoff, it can also bounce the switch causing it to arc and fuse or trip it requiring human intervention.

Good point. With a low pressure cutoff, that would be not so good. And even if it did not cut off the first several times, it might cut off when more water is being used.

My thinking for making the precharge a bit higher, if no stutter results, is that I figure it is a little easier on the pressure tank -- minimizing potential diaphragm stretch. I don't use a low pressure cutoff switch. I might if I thought I might run short of water some day, but that was unlikely enough to not spring for an electronic protector. With my regular pressure switch, I don't have to reset the switch if the power goes off temporarily while I am using some water.

 

[Johnnyh55]

so with the tank setup this way right now, what symptoms should i be experiencing that a new tank would solve? the pump is a Goulds J7S 3/4hp. will time it to see how long it takes to shut off when it starts.

 

[Reach4]

so with the tank setup this way right now, what symptoms should i be experiencing that a new tank would solve?

Fast on-off cycling.

 

[Johnnyh55]

well the pump turns on at 48psi and turns off at 68psi, I don't think that is short cycling? or am i missing something?

 

[Valveman]

well the pump turns on at 48psi and turns off at 68psi, I don't think that is short cycling? or am i missing something?

Depends on how long it takes to get from 48 to 68 according to how large the tank is (you didn't say). But short cycling with a regular tank system is anything less than 1 minute of on time and 1 minute of off time. 2 minutes on and two off is better, and running continuously while any water is being used is the best thing for the pump/motor.

Having the correct 44 or so air charge in the tank will give you the longest run time possible for the size of tank you have. Many people think letting air out of the tank makes the tank hold more water, which is NOT true.

 

[Johnnyh55]

The bladder tank is a red lion model RL20 20 gallon tank. it takes 31 seconds to go from cut-in to cut-out(48/68).

 

[Valveman]

The bladder tank is a red lion model RL20 20 gallon tank. it takes 31 seconds to go from cut-in to cut-out(48/68).

A 20 gallon size tank only holds 5 gallons of water. So 31 seconds to fill the tank would be right if you have a 10 GPM pump. If so there is no way you have zero air pressure in the tank. Sounds like the tank has the proper air charge, but it is only half the size needed to get the minimum of 1 minute run time and 4 times too small to get the preferred 2 minutes of run time. But the 20 gallon tank you have is 4 times larger than it needs to be if you have a Cycle Stop Valve or CSV. When you have a CSV to eliminate the cycling, you don't need a very large pressure tank.

 

[LLigetfa]

So 31 seconds to fill the tank would be right if you have a 10 GPM pump.

Cary, are you factoring that the OP has a shallow well jet pump? We don't know what model and from what depth it is sucking but at 68 PSI kickout, I doubt it would be moving anywhere near 10 GPM. My guess is at that pressure it is almost deadheading.

 

[LLigetfa]

it takes 31 seconds to go from cut-in to cut-out(48/68).

The time it takes depends on the pump. A better measure is a drawdown test. With no other water use in the house, measure how many gallons you can draw right after the pump shuts off until it turns back on. As Cary said, that tank should give you roughly 5 gallons.

 

[Valveman]

A J7S can pump about 12 GPM at 50 PSI and 6 GPM at 68 PSI. So I would figure an average tank fill to be about 8 GPM, which makes 30 seconds about right for that size tank.