Can You Increase Pump Head Without Changing Flow? | Liancheng Technical Window on Pump Energy Saving

A:

Customers often say things like this:

“The current flow rate is sufficient, but the pressure seems a little low. Can you increase the pressure without changing the flow rate?”

Or:

“The pressure is sufficient, but the flow rate seems a little low. Can you increase the flow rate without changing the pressure?”

So, can we meet this kind of requirement?

01

If the customer is saying:

“We previously purchased a pump from you with a head of 20 m and a flow rate of 1,000 m³/h. Now we want a pump with the same head but a flow rate of 1,250 m³/h.”

Or:

“We want a pump with a head of 25 m while keeping the same flow rate.”

Obviously, there is no difficulty with this type of request. We simply select and manufacture a pump according to the parameters provided by the customer.

However, we all know that this is probably not what the customer really means.

02

If the customer’s actual meaning is:

1. The pump currently in operation has a discharge pressure of 0.2 MPa (approximately equal to 20 m head) and a flow rate of 1,000 m³/h, but the production process feels that the pressure is sufficient while the flow rate is a little too low. Can you keep the discharge pressure at 0.2 MPa unchanged and increase the flow rate to 1,250 m³/h?

Or:

The pump currently in operation has a discharge pressure of 0.2 MPa (approximately equal to 20 m head) and a flow rate of 1,000 m³/h, but the production process feels that the pressure is not quite sufficient. Can you increase the discharge pressure to 0.25 MPa (approximately equal to 25 m head) while keeping the flow rate unchanged?

Based on the customer’s intention, we need to discuss two situations: constant operating conditions and variable operating conditions.

Constant Operating Conditions

The water demand at the process end remains basically unchanged, meaning the required pressure and flow rate remain essentially constant.

For example, a cooling tower circulating pump system:

The pump draws water from a basin and delivers it to the cooling tower.

(Process flow: Water Basin → Pump → Cooling Tower)

This is the most common type of constant operating system. The height of the cooling tower does not change, and the downstream water requirements remain unchanged.

Variable Operating Conditions

The water usage conditions change frequently, meaning the required pressure and flow rate vary according to operating conditions.

For example, the supply pump system in a municipal water plant:

The pump delivers water from the water plant reservoir to consumers.

(Process flow: Water Plant Reservoir → Supply Pump → Consumers)

The main characteristic of this system is that end-user demand changes constantly, especially the flow rate.

① Constant Operating Conditions

When system demand remains basically unchanged, can the customer’s request be achieved?

Definitely not.

In more technical terms, after the pump performance curve and the system resistance curve are re-matched, both the actual flow rate and head will change. It is impossible for one parameter (either head or flow rate) to remain unchanged while the other changes.

In other words, the customer’s requirement is contradictory and cannot be achieved.

Customers may say they have seen this happen elsewhere and question your technical capability. If you can explain the principle clearly, that is ideal. If not, feel free to contact our specialists for assistance.

② Variable Operating Conditions

When system demand changes frequently, can the customer’s request be achieved?

Yes, it is generally possible.

This is most commonly seen in municipal water supply systems. Supply pumps are usually designed to maintain a constant discharge pressure while the flow rate adjusts automatically according to consumer demand.

Of course, simply replacing the pump alone cannot achieve this type of real-time adjustment. A Variable Frequency Drive (VFD) must be installed to assist.

There are also other variable-process applications where a constant flow rate is required while pressure changes according to operating conditions. In these cases, replacing the pump and adding a VFD are also necessary.

Summary

Under constant operating conditions, the customer’s requirement cannot be met.

Under variable operating conditions, the requirement can be met.

Therefore, it is essential to fully understand the customer’s process and operating conditions before proposing a solution.

For a more detailed explanation of the principles and implementation process, please contact Liancheng Pump Energy Saving Department at +86-21-5913-2577.