# Thread: pumps in parallel

1. ## pumps in parallel

When running pumps in parallel, do they need to be at the same psi?

2. ## Re: pumps in parallel

Welcome to TFP!

psi isn't a pump specification, it is the result of the combination of a pump and a plumbing system.

When running pumps in parallel they need to be matched pumps (same size, same design) with piping the same size and same length.

3. ## Re: pumps in parallel

Pumps running in parallel have no choice but to run at the same PSI. The point where they combine has to be at the same PSI because it is a common node.

However, you can run pumps in parallel of different sizes although the smaller pump will produce much less flow rate because both pumps see the same head loss that is created by both pumps. So the combined flow rate of both pumps is less than the sum of the individual flow rates when run separately.

4. ## Re: pumps in parallel

Ok thanks, the gauges on both pumps (which are the same size amp/volt and make) have guages that are reading differently. The first pump to pull off of the main pipe is reading 25 psi, the second off of the same pipe is reading 5-7 psi. My flow rate is about 1500-1700 when the butterfly valves are open about 50%. How can I correct the difference in psi.

5. ## Re: pumps in parallel

The pumps might be the same in amp/volt and make (that is, they use the same motor) but one of them might be a pressure pump (high pressure with less flow) and the other might be a high flow pump (high flow with less pressure).

Take a look at the impellers of these pumps if no flow/pressure chart is available.

Assuming both are pressure pumps (or both are high flow pumps), then take a look at the geometry of the pipes feeding and exiting the pumps, until the point where these pipes meet, you should see a mirror image, leading to a Y connector (top of Y comes from each pump, bottom of Y is combined exit).

Even better, post some pics.

6. ## Re: pumps in parallel

One or both of the gauges are broken. The pressure must necessarily be the same if their outputs are connected together.

7. ## Re: pumps in parallel

Where are you measuring pressure in relationship to where the flows combine? Or do the flows never combine?

If they are feeding different return pipes, then it doesn't matter.

8. ## Re: pumps in parallel

Are their outputs connected together? Just making sure they are truly in parallel.

If they both draw from the same intake system yet have different paths to the pool it is possible for the situation you currently observe to be normal and everything is working correctly.

For example, main pump and a water feature pump that is plumbed separately from the filtration system.

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