Is a pressure tank necessary if I have a large cistern before the jet pump?

[Suceress]

I am guessing the answer is "yes" but I just wanted to make sure.

My system is that I have a pneumatic pump with two wheels that forces air down into the underground well (it is maybe 1" or 3/4" pipe). If there is any sort of pump underground I do not know. This system was in place when we bought the house in the 80s.
The water comes up a maybe 2" or 3" PVC pipe, elbows, and attaches to the lid of a fiberglass cistern. My guess is the cistern is at least 500 gallons if not more. A D switch with float tells the pump to turn on or off.

A pipe comes out of the lower part of the cistern (horizontally) and routes to a 1hp jet pump which has a 30/50 pressure switch. From there a pipe comes out the top & has a pressure gauge and then loops around to a fiberglass pressure tank. From the pressure tank, it reduces to 3/4" pipe (it's 1" coming out of pump and going in to tank) and then goes to the house.

Since the cistern holds the water & the jet pump has a pressure switch, does that mean the pressure would still be consistent without the tank? I'm trying to figure out what purpose the tank has.

Not sure on the size of the tank, but it's relatively large. I'll have to dig up photos later.

Is this pressure tank even needed? If so, why? (to regulate pressure?)

As it is, my current setup leaves me with air bubbles that cause the water to spurt (they installed the intake line on the pump in such a way that it loops above the pump-- I have tried correcting this but it didn't work & the guy who works on the pumps put it back the way it was but removed the shut-off before the pump so I can't work on the pump without draining the cistern first). Most of the pipes are PVC with a little bit of stainless steel that I added on the intake side of the pump because it kept melting/breaking the PVC. Galvanized pipe comes out the top and then goes to PVC. It's a hot mess.

 

[LLigetfa]

The pressure tank is essentially a timer that ensures the pump does not short-cycle. It is often sized so that the pump runs for a minimum of 1 or 2 minutes.

 

[Sponsor]

 

[Suceress]

If I understand correctly, the pressure tank holds excess water so when it is empty the pump will turn on to refill it, but will not have to turn on every time water is used? I know sometimes water does flow even when my pump is off, but I don't know if that is from the force of water coming out of the cistern or what. I want to have a better understanding of how the system works.

I know Valveman has been encouraging me to get a cycle stop valve setup.

 

[LLigetfa]

I know sometimes water does flow even when my pump is off, but I don't know if that is from the force of water coming out of the cistern or what.

It is the force of compressed air in the pressure tank that expels water under pressure. The cistern gravity pressure is only 0.43 PSI per foot of elevation.

 

[Bannerman]

Pump's are designed to run continuously 24/7. It is repeated cycling On & Off, especially within short time frames that will shorten the lifespan of the pump, pressure switch, pressure tank etc.

Because most people do not use water 24/7, then there would be no purpose or benefit to running the pump continuously while there is no water needed.

The purpose for the pressure tank is to reduce cycling by ensuring the pump will operate for a specific minimum period of time once activated. The usual minimum recommended time for the pump to operate once activated is 60 seconds, but 120 seconds would be better, but running non-stop would be best.

For instance, if your pump will deliver 10 GPM, to achieve 60 seconds run time, the pressure tank would need to hold 10 gallons water from when the pump is activated, to when it is shut off. Since approx 3/4 of the pressure tank will contain air that will be compressed to push the water out while water is drawn before the pump becomes activated, the total tank size will be 40 gallons. For 120 seconds run time, 20 gallons water = 80 gallon tank.

When less water is consumed than the pump can deliver, then the excess pump capacity will flow into the pressure tank. (10 GPM from pump, shower flowing 3 GPM = 7 GPM into PT). Once the system pressure rises to the pressure switch cut-out pressure (ie: 60 psi), then the pressure switch will shut off the pump. The PT will then continue to supply water to the shower, but the pressure will drop until the PS will reactivate the pump at 40 psi. This cycling will continue to occur until no water continues to be drawn OR, there is additional water flowing to faucets to match the pump's delivery rate (10 GPM) so there will be no excess water from the pump.

Valveman's Cycle Stop Valve is a mechanical device that will cause the pump to only deliver the exact amount of water that is being utilized. If there is 3 GPM flowing to the shower, then the CSV will cause a 10 GPM pump to deliver only 3 GPM. If someone flushes a toilet that fills at 2 GPM while the shower is running, then the CSV will immediately cause the pump to deliver 5 GPM while maintaining constant pressure to both the shower and toilet.

Because a CSV will cause the pump to deliver 1 GPM once no furthet water is being utilized, a very small pressure tank (4 gallon total = 1 gallon water) is usually all that is needed to ensure the pump will operate for at least 60 seconds.

 

[Suceress]

Thank you very much for the responses!
I wish prices hadn't gone so high on things because I would like to change my setup, but it is going to be difficult since the guy who does repairs on the pump removed the shutoff. I do plan to get at least some sort of CSV at some point.

I've talked to Valveman online and he's given me some guidance on how to set things up, but I need to refresh my memory.

So, my understanding is Yes, I need a pressure tank. LOL.