What sort of pump does a swimming pool waterfall need?

Choosing the right one pool waterfall pump It is essential for achieving a continuous, even stream of water that is proportionate to the size of the waterfall.

Before sizing the pump, it is also advisable to check the main criteria for selecting and installing a laminar flow cascade, such as width, drop height, levelling and the type of hydraulic circuit.

It is not enough simply to choose a pump based on its power in CV, nor is it sufficient to use the model installed for filtration. To size the equipment correctly, you need to know the flow rate required by the waterfall, calculate the manometric head of the system and check the pump’s performance curve.

An under-sized pump can result in an irregular or intermittent water flow. Conversely, an over-sized pump can cause splashing, noise, unnecessary energy consumption and difficulties in regulating the flow.

In this guide, we explain which factors you should consider when choosing the right pump for a swimming pool waterfall.

What information do you need to choose the right pump?

One of the most common mistakes is to ask how many horsepower a waterfall requires without taking the rest of the installation into account.

The pump’s power rating is an important figure, but on its own it does not tell you how much flow the pump will deliver once it is connected to the pool’s pipework, valves and fittings.

Two pumps with similar power ratings may have different hydraulic curves. This means that they may deliver different flow rates when operating at the same head.

For this reason, the selection should be based primarily on two pieces of data:

• The flow rate required by the waterfall.
• The total manometric head of the system.

How much flow rate does a swimming pool waterfall require?

Flow rate indicates the volume of water circulating through the system over a given period. In swimming pool systems, it is usually expressed in cubic metres per hour, denoted as m³/h.

Every waterfall requires a certain flow rate to form the water curtain properly. This figure depends on factors such as:

• The width of the exit.
• The interior design of the waterfall.
• The shape of the discharge outlet.
• The desired sheet thickness.
• The height from which the water falls.
• The intended visual effect.
• The manufacturer’s instructions.

A wider waterfall usually requires a greater flow rate than a smaller one, but one should not automatically assume equivalence based solely on external dimensions.

Two waterfalls of similar size may have different hydraulic requirements. Therefore, the first step should be to consult the model’s technical data sheet and identify the recommended flow rate.

Each model may require a different flow rate. Therefore, before selecting the pump, it is advisable to identify the size and configuration of the sheet metal waterfalls for swimming pools to be used in the project.

What is manometric head?

The manometric head represents the resistance that the pump must overcome in order to transport the water from the suction point to the outlet of the waterfall.

It should not be confused with the depth of the pool, nor should it be limited solely to measuring the height of the waterfall.

To calculate the total manometric head, the following must be taken into account:

• The difference in height between the water level and the top of the waterfall.
• The total length of the pipes.
• The internal diameter of the pipes.
• Bends and changes of direction.
• Valves and control components.
• T’s, contractions and conjunctions.
• Losses occurring in the suction system.
• Pressure losses in the discharge line.
• The minimum pressure required by the cascade, where specified by the manufacturer.

The greater the resistance in the circuit, the lower the flow rate the pump will be able to deliver.

How to calculate the pump size for a swimming pool waterfall

The selection process must follow a structured procedure.

1. Check the required flow rate

The first step is to work out how many cubic metres per hour the waterfall needs to produce the desired water curtain.

This information must be obtained from the technical documentation for the specific model.

It is not recommended to estimate this based solely on the width of the waterfall.

2. Measure the height of the installation

The vertical difference between the level from which the water is drawn and the point where the waterfall flows out must be calculated.

In most projects, the water is drawn from the pool itself or from a circuit connected to the pool and is pumped up to an outlet situated above the water surface.

3. Check the pipes

You need to know:

• Suction length.
• Drive length.
• Pipe diameter.
• Number of bends.
• Number of valves.
• Existence of reductions.
• Possible changes to the section.

A pipe with an insufficient diameter can result in high pressure drops and restrict the cascade’s performance.

4. Calculate the total manometric head

The pressure losses caused by the pipework and fittings must be added to the geometric head.

Where the manufacturer specifies a minimum operating pressure, this must also be taken into account.

5. Check the pump curve

Once the flow rate and head are known, the pump’s hydraulic curve should be checked.

In this graph:

• The horizontal axis usually represents the flow rate.
• The vertical axis represents the manometric head.
• The curve shows how much flow the pump can deliver at each head.

The operating point must lie within the curve of the selected model.

Performance curves relate the flow rate, usually denoted as Q, to the head or pressure generated by the pump, denoted as H. Both variables must be analysed together when sizing the equipment.

Why should the pump’s maximum flow rate not be used?

Many product data sheets feature a maximum flow rate. However, this figure does not mean that the pump will deliver that flow rate in every installation.

The maximum flow rate usually corresponds to conditions where there is little hydraulic resistance. As the manometric head increases, the available flow rate decreases.

It is therefore not enough simply to check that the pump’s maximum flow rate exceeds that required by the cascade.

It must be verified that the pump delivers the required flow rate at the head calculated for the project.

Can the filter pump be used for the waterfall?

In certain installations, it is possible to connect the cascade to the filtration pump circuit.

To achieve this, a diversion is usually created using a valve that allows part of the flow to be channelled towards the waterfall.

This solution may be appropriate when:

• The filter pump has sufficient flow rate.
• The filter continues to work properly.
• The pipes are sized for the total flow rate.
• The waterfall does not require a particularly high flow rate.
• The water distribution can be adjusted.
• The waterfall will be in operation from time to time.

However, opening a bypass to the waterfall reduces the flow available at the other discharge outlets.

If the pump is rated solely for filtration, it may not have sufficient capacity to supply both circuits simultaneously.

It should also be noted that the waterfall will only operate when the filter pump is switched on, unless the control system is modified.

When should you install a stand-alone pump?

Installing a separate pump is usually the most suitable solution when the cascade has a high hydraulic demand or when it needs to be controlled separately.

This type of installation allows:

• Switch on the waterfall without activating the filtration system.
• Adjust the water effect independently.
• Avoid any changes to the main circuit.
• Select a specific pump for the required flow rate.
• Install a dedicated switchboard or push-button switch.
• Control several waterfalls or water features.
• To facilitate maintenance of the auxiliary circuit.

Trypool offers single-speed and variable-speed self-priming pumps for various types of installations. When selecting a model, you should check its performance curve and operating point, not just the power rating stated in the technical data sheet.

Electrical control panels fitted with piezoelectric push-buttons can also be used to control the operation of a stand-alone pump. Trypool offers solutions designed for controlling pumps for waterfalls, jets and other aquatic features.

When the waterfall incorporates a separate pump, a electrical control panel with piezoelectric control for pumps

In systems with a dedicated circuit, a pump must be selected that is capable of delivering the required flow rate at the actual operating point. You can view the range of self-priming pumps for swimming pools from Trypool and check the performance curves for each model.

Fixed-speed or variable-speed pump

Both options may be suitable provided they deliver the required flow rate and head.

Fixed-speed pump

A single-speed pump operates at a fixed speed.

It can be a simple solution when:

• The cascade has a single operating point.
• The required flow rate is clearly defined.
• Adjustment can be carried out hydraulically.
• There is no need to adjust the effect frequently.

The pump must be selected with a suitable performance curve to avoid either excessive or insufficient flow.

Variable-speed pump

A variable-speed pump allows the operating speed to be adjusted and the flow rate to be adapted.

It may be useful when:

• We want to adjust the intensity of the waterfall.
• There are various water-based effects.
• The installation operates under a variety of conditions.
• More flexible regulation is needed.
• The aim is to reduce consumption when it is not necessary to operate at full capacity.

Speed control is no substitute for hydraulic calculation. The model must still be capable of reaching the required operating point.

Common mistakes when choosing a pump

Choosing a pump based solely on horsepower

Power does not indicate the flow rate available at the actual operating point.

Do not refer to the technical data sheet for the swimming pool cascade pump

Each model may require a different flow rate.

Use the maximum flow rate specified in the catalogue

The maximum flow rate does not necessarily reflect the performance taking into account the system’s pressure drops.

Installing a pipe that is too small

A small cross-sectional area can restrict the flow rate and increase consumption.

Adding too many bends

Changes in direction increase pressure drops.

Do not fit a regulator

Without a suitable valve, it can be difficult to adjust the water level.

Oversizing the pump for a swimming pool waterfall

A pump that is too large can cause splashing, noise and an uneven result.

Always blaming the pump for an uneven finish

An irregular discharge may also be caused by:

• A waterfall with varying heights.
• Dirt at the outlet.
• Uneven distribution of water.
• Air in the pipe.
• Blockages.
• Incorrect installation.

Do you need to select the right size of pump for a waterfall? Contact Trypool’s sales department and specifies the cascade model, the height, the distance to the plant room and the planned specifications of the circuit.