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It's one of those pieces of advice that gets passed around time and again: "if you
want to change the flow rate, just adjust the bypass”.
It sounds reasonable. Unfortunately, it's a myth.

What is the bypass actually for?

The pressure relief bypass is not a flow control device. It is a safety valve.
On Silea Liquid Transfer pumps, it is typically factory-set to 3.5 bar and has one specific
purpose: preventing the system pressure from exceeding a predefined limit.
When that pressure is reached, the bypass automatically opens, bringing the pressure
back within the safe operating range and protecting the entire system.

Why shouldn't it be used to regulate flow?

Adjusting the bypass will not increase or decrease the pump's flow rate.
If you need to modify the flow, the correct approach is to adjust the motor speed, because
the bypass was never designed for flow regulation.
Changing its setting in an attempt to control flow means interfering with a component
whose primary role is to keep the system safe.

What happens if it's adjusted incorrectly?

An improperly set bypass can lead to serious consequences.
• If the bypass is set too high, it may fail to open during an overpressure event. This can
result in water hammer — sudden pressure spikes capable of damaging pipes and other
system components.
• If it is set too low, the pump may operate with the bypass continuously open. When
handling gasoline or certain solvents, this can lead to the continuous release of vapours,
creating unnecessary safety risks.

The right solution

If your goal is to regulate the flow correctly, adjusting the bypass is not the answer.
To accurately control inlet and outlet flow, Silea Liquid Transfer recommends using the
Avery Hardoll IPV valve in combination with an electronic register. This configuration
ensures effective flow control while also helping protect the system against water hammer.
The bottom line? The bypass is not a flow regulator — it's the pump's silent guardian. And,
like any safety device, it performs best when it's left to do the job it was designed for!