Just a general question about water pumping

Saffa said:

If there is sufficient storage in the tank that the pumps draw from, you can calculate a rough flow rate by stopping flow into the tank, and recording change in level over time. Assuming accurate measurements are possible from a sight glass or gauge.

Then flow rate = volume change over time. Do it in minute intervals if possible to measure level accurately.

Have excluded units as I can only understand that crazy metric system stuff and not the foot-pounds per square barrel of grandmas type units you guys over that side of the world use.

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We use Budweisers per Freedom Eagle.

sparkie said:

We use Budweisers per Freedom Eagle.

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No idea how to convert it, but I'll drink to that.

"Towel" was supposed to be "tower".

If all you have is a pressure gauge then use a constant pressure horizontal line as the system curve. That is probably the objective of the control system anyway.

These sites may help you too: https://www.engineeringtoolbox.com/
https://www.engineeringtoolbox.com/pump-system-curves-d_635.html
https://www.engineeringtoolbox.com/pumps-parallel-serial-d_636.html

sparkie said:

How would I go about making a system curve or getting the necessary information?

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Some things to consider:

The best place to start is with the pump curves. If they don't have the records, which may be outdated by upgrades that weren't documented, inquire with the pump manufacturer. They should have curves for pump model/impeller size and speed.

Ideally, the pumps and their impellers are identical and thus have identical curves. Assuming that's the case, there are two running scenarios: one pump running with the other off OR both running at the same speed. The 2-pump-running condition must have both pumps operating at the same discharge pressure; is this wasn't the case, one pump would generate no flow or exhibit cycling/chattering of the check valve seen at the pump's discharge.

The pump curves would be instructive in determining when to transition from 1 to 2 pumps, then back to 1 again. (And the reason this is presently a need is because your client currently has higher demand than a single pump can offer and because they want increased turndown of the system).

Feedback control is similar to how operated currently: discharge pressure is controlled by pump speed. When (at what pressure/speed combinations) and how to gracefully transition between 1 and 2 pump operation is the challenge. Pump curves should give insight to the 'when' question.