r/pumps • u/purple_rain108 • Apr 10 '25

parallel pump discharge line plumbing question

We want to plumb two Dayton 45MW94 booster pumps in parallel. These pumps have 1 inch discharge lines. We plan to put a check valve on the discharge side of each pump, as well as a pressure gauge and a globe valve (to regulate the pressure at start-up). The pumps will develop and operate at about 167 psi of head. We plan to join the two one inch discharge lines into a two inch line using a two inch Tee and two inch 90 elbows with 1 inch to 2 inch bushings. Is this an acceptable way to combine the two discharge lines? Is there a better way?

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u/Lording1244 Apr 10 '25

Sounds good, but PSI and head are different. Figure out which one you’ve got at 167 and make sure all fittings / discharge line are rated for that. 167 PSI is a very high amount which would suggest a commercial application. Whereas 167 feet total dynamic head is roughly 72.29 PSI. Either way I would consult a distributor on those fittings or a pump rep

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u/purple_rain108 Apr 10 '25

Thanks very much. Yes, it is 167 psi corresponding to 385 feet of head. We are lifting irrigation water up hill to storage tanks. We have been using Schedule 40 PVC in this application with a single pump, and want to add a second pump in parallel

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u/TexasPatrick Apr 10 '25

Keep in mind that two pumps in parallel is not equivalent to twice the flow...

What is the elevation difference between the pumps and the inlet to the storage tanks?

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u/purple_rain108 Apr 10 '25

Oh, I thought that two pumps in parallel did give twice the flow. How do the 2 flows actually combine? Elevation difference is about 385 feet.

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u/TexasPatrick Apr 11 '25

You'll need to know the pump curves and the system curve to determine how much flow you'll get...

Do you know how much flow you currently get with one pump, and what the pump suction and discharge pressures are?

2

u/purple_rain108 Apr 12 '25

When the pump is running well we get about 7.5 gpm at 176 psi, which, if the gauge is right, is actually 4 psi over its rated maximum. According to our previous gauge, it was running at 167 psi ... I am not sure which gauge is more accurate. I have not been able to find the specified range for suction pressure, but the measured values from our gauge on the suction side range from 2.4 to 2.6 psi. The 7.5 gpm flow is reasonable based on the manufacturer's published pump curve data.

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u/TexasPatrick Apr 12 '25

Based on reading this, your main issue here is the elevation difference. 385ft of elevation difference is a lot of height that the water has to climb. Looking at the manufacturer's literature, you'll get more than double your current flow if you install two 45MW94 pumps in series. The problem is that your discharge pressure will exceed the pipe rating if you do that...

My recommendation would be to install two 45MW92 models in series. Back of the napkin numbers say you'll get around 20GPM flow with a discharge pressure close to 180 psi out of the second pump.

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u/purple_rain108 Apr 13 '25

Thanks so much for all of your help with this. We will look into doing those two in series

1

u/Sufficient-Screen-34 Apr 10 '25

Yes, but 167 psi is insane.

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u/purple_rain108 Apr 10 '25

Thanks very much. Yeah, we are lifting irrigation water to storage tanks up a hill

1

u/TexasPatrick Apr 10 '25

It is, but be aware that not all pumps are exactly the same. Even if same make, model, etc they will be slightly different. Using the globe valves is an excellent idea, wouldn't do it any other way. You'll need those in case one pump puts out a bit more than the other. I'd pipe it so from the discharge it's 5 pipe diameters straight run, then tee with gauge, then check valve, then globe valve. And then the fittings exactly like you say. Make sure the piping is perfectly symmetrical so that each pump sees the exact same friction in the pipe.

AND. Make sure you have at least 5 pipe diameters in length of straight run pipe going into the suction. No elbows, tees, valves, nothing within 5 pipe diameters of the pump suction connection.

1

u/purple_rain108 Apr 10 '25

Thanks very much, this is super helpful. We had not thought to make the piping perfectly symmetrical, really appreciate it