New pump will not build pressure

[DPForumDog]

Pump is not building pressure. Would a check valve on the suction side near the pump cause prime problems?

We are trying to pump pond water for irrigation. I have a foot valve in the pond and then 70 ft of 2" pipe going to the shed where I have a Red Lion 77 GPM 2 HP Self-Priming Cast Iron Sprinkler Pump w/ Brass Impeller (RL-SPRK200-BR). There is about a 5 ft rise over that 70 ft.

Originally i had the check valve on the down stream of the pressure switch but every time the pump shut off the pressure would drop below 20 lbs, and the pressure switch in the auto function shuts off and want come back on until its manually moved to start. So I changed the check valve to the suction side.

I would appreciate any ideas.

Thanks
Granny DP
DPForumDog

 

[Valveman]

With 5' of lift that pump can only build 45 PSI against a fully closed valve. But it will still do about 50 GPM at 40 PSI. Most likely you have a small leak in that 70' of suction line. The shorter the suction line on a pump like this the better. Don't count on it "self priming". You will need to fill the entire 70' line with water before starting the pump. Even then, the smallest leak in the suction will make it loose prime. Any union or threaded fitting in the suction line is suspect.

 

[Sponsor]

 

[DPForumDog]

I think the only union or threaded fitting we would have is the check valve which is right by the pump or possibly at the foot. Ill ask my husband.
This may be a clue .... we can take a garden hose with city water down to the foot and it works perfectly.
Thank you for your response.
Granny DP
DPForumDog

 

[Reach4]

This may be a clue .... we can take a garden hose with city water down to the foot and it works perfectly.

Could you clarify that sentence?

 

[Fitter30]

You can't suck water 70' pump is only rated for 25'. 28' is max on any pump with perfect conditions. Read the spec in your manual.

 

[DPForumDog]

We had two valves, We removed the check valve by the pump and left the foot valve and the pump is now working. The flow is amazing, But I think we are going to have to play with the adjustment on the pressure switch, but so far so good. I'll keep you posted. Thanks Everyone.

p.s. maybe we had the wrong type check valve, maybe we needed a spring type check valve instead of the flapper style with the union.

 

[DPForumDog]

You can't suck water 70' pump is only rated for 25'. 28' is max on any pump with perfect conditions. Read the spec in your manual.

Thank you, I must not understand the definition of " Suction Head ". I thought suction head was the height difference between the foot in the pond and the pump? There is a only a 5ft rise over the 70 feet so I thought that 5ft was our suction head.

We have a foot valve in the pond and then 70 ft of 2" pipe going to the shed where I have a Red Lion 77 GPM 2 HP Self-Priming Cast Iron Sprinkler Pump w/ Brass Impeller (RL-SPRK200-BR). There is about a 5 ft rise over that 70 ft.

This was the pump that Pumps Direct recommended, we may have to consider a bigger pump?

Thanks Again!
Granny DP
DPForumDog

 

[DPForumDog]

Could you clarify that sentence?

We put a "T" with a shutoff valve close to the the foot. This allows us to connect city water via a garden hose to push out air. This forces the air out.

 

[Fitter30]

Long suction line fiction and cavitation is your enemie. Fiction trying to suck water thru longer than design pipe. Cavitation occurs when pockets of air or vapour are created within the fluid due to pressure changes. These tiny bubbles then implode, releasing a shockwave and causing damage to surrounding parts, including the impeller. A short and direct suction line reduces the risk of cavitation.

 

[Reach4]

1. Do you have a pressure tank at the pressure switch? If you use a pressure switch, you need a pressure tank.
2. Does the pump pump water when the switch turns back on?

 

[DPForumDog]

1. Do you have a pressure tank at the pressure switch? If you use a pressure switch, you need a pressure tank.
2. Does the pump pump water when the switch turns back on?

1. No we don't have a a pressure tank. But my husband has thought about adding one,
2. Yes.

 

[DPForumDog]

Long suction line fiction and cavitation is your enemie. Fiction trying to suck water thru longer than design pipe. Cavitation occurs when pockets of air or vapour are created within the fluid due to pressure changes. These tiny bubbles then implode, releasing a shockwave and causing damage to surrounding parts, including the impeller. A short and direct suction line reduces the risk of cavitation.

I don’t think it is cavitation, All the air is out. When the pump shuts down the pressure varies. The needle will read from 40 to 60 lbs.. ( needle bouncing back and forth.)
It easily pushes water 1000 ft over a 25 ft rise, but you do have to open two valves or the pump just cycles off and on,
My husband thinks he needs to reinstall a check valve but this time a spring style , not a flapper style. And maybe add a pressure tank?
Thanks for all ideas!

 

[DPForumDog]

We are wondering if the water weight pushing back on it is a problem. Maybe if we had a check valves at 500 ft of the 1000 ft. ?(down stream side!!) Or maybe multiple check valve. That may not help the pump cycling but it might keep the needling from going from 40 to 60. Pressure bouncing.

 

[LLigetfa]

Don't add a second check valve on the suction side. You do need a pressure tank as the intake line swells when changing from suction to pressure when the pump turns off. Maybe a pressure switch is not the way to go if you cannot prevent the pump from cycling. Can your irrigation controller turn the pump on and off by relay?

 

[Bannerman]

Water cannot be compressed so without a pressure tank, once the pump is shut off, there is nothing to maintain pressure in the system.

A captive charge pressure tank utilizes an air chamber that is separated from the water chamber by a flexible synthetic rubber diapghram or bladder. The air in the chamber is compressed to a pressure slightly lower than the pressure switch setting so only a minimal amount of water will be contained in the tank at the pressure switch cut in pressure.

When the pump is operating, water will enter the tank under pressure which will place force on the diapghram which will further compress the air in the air chamber so the pressure in both chambers will then be equal. Once the pressure rises to the PS cut out pressure, the pump will shut down. With a properly functioning footvalve, the force of the compressed air against the diapghram against the water will maintain the pressure on the water side even while the pump is not operating.

 

[DPForumDog]

Water cannot be compressed so without a pressure tank, once the pump is shut off, there is nothing to maintain pressure in the system. .

Thanks.
I now see the water does NOT flow thru a pressure tank,With a 2” inlet/outlet I was worried it euros restrict our flow?

 

[DPForumDog]

What size pressure tank should we get?
Pump is 70 ft suction line to lake, with a slight 5 ft rise over the 70 feet.

distribution side:
The pump then pushes water almost 1000 ft with about a 25 ft incline,

the system works great now, but the pressure needle bounces. I water today fir a couple of hours. But I agree we need a pressure tank.
Thanks
Granny DP
DPForumDog

 

[LLigetfa]

If the pump is not cycling when water is in use, then you don't need a very large tank. A 10 or 20 gallon tank would buffer the fluctuation and provide enough volume to hold the pressure high enough when the pressure switch turns off the pump.

If however, you cannot prevent the pump from cycling during water use, then the bigger the better.

 

[Bannerman]

Water does not flow through a pressure tank as it will only store a small amount of water relatively speaking, The water will continue to come from the well and pump for delivery to your existing plumbing, but the pressure tank will ensure the system will continue to be pressurized within the intended operating pressure range. If for example, you are using a 20/40 psi pressure switch, while the pump is running, the system pressure will rise to 40 psi and the pump will then shut off. Any further water use will cause the pressure to be reduced and once lowered to 20 psi, the pump will be activated again. The air in the air chamber becomes compressed similar to a spring while the pump is running and water is entering the tank, and that compressed air will push the water back out while water is being consumed before the pump is activated.

Because most pumps are designed to run continuously, there is little harm in operating a pump for long periods, but repeated ON/OFF cycling are most damaging, especially when occurring within a short period of time. The recommended pressure tank size will be mainly determined by the pump flow rate. The correct size will cause the pump to run continuously for 60-120 seconds after there is no further water use. This amount of run time will reduce cycling but will not eliminate it while less water is being used than the pump can deliver.

To eliminate cycling, Valveman's Cycle Stop Valve device should be utilized. In the 20/40 psi pressure range example, once the pump is operating at 20, the system pressure will rise to 30 psi, causing the CSV to regulate the flow from the pump to maintain that 30 psi constantly. Once there is no further water use, the CSV will then fill the pressure tank to 40 psi while allowing only 1 GPM to pass through. Because the tank fill rate is only 1 GPM, a 4.5-gallon tank which will hold a little more than 1-gallon, will be suitable for most residential applications while still providing 60+ seconds minimum run time.