Pool plumbing is the pipe network connecting every component in your system: skimmer, main drain, pump, filter, heater, salt chlorinator and return jets. In most European residential pools, PVC pressure pipe in 50 mm or 63 mm diameter is the standard. Choosing the right diameter, gluing joints correctly and designing sound hydraulics determine whether your system runs smoothly or constantly struggles with insufficient flow.
Which PVC diameter should you choose for your pool?
The two common diameters for residential pools are 50 mm and 63 mm (outer diameter). The choice depends on your pump’s flow rate and the total pipe run length.
Flow capacity per diameter
| Diameter | Max. recommended flow | Water velocity at max. flow |
|---|---|---|
| 50 mm (inner diameter 43.4 mm) | 10 m3/hr | 1.9 m/s |
| 63 mm (inner diameter 55.4 mm) | 16 m3/hr | 1.8 m/s |
| 75 mm (inner diameter 66.0 mm) | 25 m3/hr | 2.0 m/s |
The rule of thumb: keep water velocity below 2.0 m/s on the pressure side and below 1.5 m/s on the suction side. At higher velocities, friction loss increases exponentially and you get audible flow noise in the pipes.
When to choose 63 mm over 50 mm
Choose 63 mm in these situations:
- Your pump delivers more than 12 m3/hr.
- Total pipe length (suction plus pressure side) exceeds 15 metres.
- You have more than 6 elbows of 90 degrees in the system.
- You are connecting multiple devices in series (filter, heat pump, salt chlorinator, UV).
For a small above-ground pool with a pump rated at 4 to 6 m3/hr and short pipe runs, 50 mm is more than adequate.
Suction side versus pressure side: what is the difference?
Pool plumbing is divided into two zones, separated by the pump.
The suction side (before the pump)
The suction side runs from the skimmer and main drain to the pump. This section operates under negative pressure: the pump draws water in. Any leak on the suction side draws air in rather than leaking water out. Air ingress is the most common cause of pump problems.
Rules of thumb for the suction side:
- Keep the suction pipe as short as possible (maximum 5 to 8 metres).
- Use as few elbows as possible (each 90-degree elbow costs approximately 0.3 metres of head).
- Position the pump no more than 1 metre above the water level—lower is better.
- Prefer 63 mm pipe on the suction side, even if the pressure side is 50 mm.
The pressure side (after the pump)
The pressure side runs from the pump through the filter, heater and any treatment equipment to the return jets. This section operates under positive pressure: the pump pushes water through. Leaks on the pressure side allow water to escape.
The working pressure of standard PVC pressure pipe (PN10) is 10 bar at 20 degrees Celsius. A pool pump delivers a maximum of 1.0 to 1.5 bar, so you have ample margin.
How to glue PVC pipes correctly
Gluing PVC is a chemical process: the adhesive (technically a solvent cement) dissolves the outer layer of the PVC. When two parts are pressed together, the surfaces fuse and form an inseparable bond after curing.
Materials needed
- PVC cleaner (primer)
- PVC solvent cement (Tangit or equivalent, rated for pressure pipe)
- Deburring tool or file
- Clean cloth
Steps for a leak-free joint
- Cut the pipe square with a PVC pipe cutter or fine-toothed saw.
- Deburr the outside of the pipe and the inside of the fitting with a file or deburring tool.
- Clean both surfaces with PVC cleaner and allow 30 seconds to dry.
- Apply a thin, even layer of solvent cement to the outside of the pipe and a thinner layer inside the fitting.
- Push the pipe into the fitting with a quarter turn until it bottoms out. Hold for 30 seconds.
- Wipe off excess cement immediately with a clean cloth.
The joint is handleable after 2 hours and fully cured after 24 hours at 20 degrees Celsius. Do not glue PVC below 5 degrees—the cement will not cure properly.
Tip
Pressurise the pipe system to 2 bar with air for 24 hours before backfilling or pouring concrete. Check the gauge after 24 hours: no pressure loss means leak-free. This saves enormous amounts of digging later.
When to use threaded connections
Threaded connections (BSP—British Standard Pipe) are used where you need to be able to disconnect equipment without cutting pipe. Typical locations include:
- Pump inlet and outlet
- Filter multiport valve
- Heat pump connections
- Salt chlorinator connections
Always use a 3-piece union (also called a barrel union). It consists of two fixed halves and a loose nut. You can open the connection without moving the pipe. Wrap PTFE tape (Teflon tape) 5 to 8 times around the thread for a watertight seal.
Basic hydraulics: calculating resistance in your plumbing
The pump must have enough “head” to overcome the total resistance of the system. Too much resistance means too little flow, which leads to inadequate filtration and heating.
Resistance sources in your system
| Component | Resistance (metres of water column) |
|---|---|
| Sand filter (clean) | 0.3 to 0.5 mWC |
| Sand filter (dirty) | 0.8 to 1.2 mWC |
| Heat pump | 0.2 to 0.5 mWC |
| Salt chlorinator | 0.1 to 0.2 mWC |
| UV system | 0.1 to 0.3 mWC |
| 10 metres straight pipe (50 mm) | 0.3 to 0.5 mWC |
| 90-degree elbow | 0.05 to 0.1 mWC |
| Tee | 0.1 to 0.2 mWC |
The total system resistance for a typical pool with a sand filter, heat pump and 20 metres of pipe amounts to 2 to 4 metres of water column. Your pump must have a head rating higher than this total resistance at the desired flow rate.
Equivalent pipe length method
A handy shortcut: count every 90-degree elbow as 1.5 metres of additional straight pipe and every tee as 3 metres. Add these to the actual pipe length to get the “equivalent pipe length”. Use this value on your pump’s performance curve to read off the actual flow rate.
Typical pool plumbing layout
The order of components in the return line matters. Here is the standard plumbing layout for a complete pool system:
- Skimmer and main drain (suction side, optionally with a three-way valve)
- Filter pump with strainer basket
- Sand filter or cartridge filter with multiport valve
- Heat pump (via bypass)
- UV disinfection (optional, via bypass)
- Salt chlorinator (last in line, via bypass)
- Return jets in the pool wall
Each optional device gets its own bypass so you can isolate it for maintenance or in case of failure. Read more about the complete water circuit and about choosing the right pump .
What is a bypass and how do you build one?
A bypass is a diversion with three ball valves in an H-shaped configuration. Water flow can be directed through the device, partially through it, or entirely around it.
Why is a bypass necessary?
A heat pump typically has a maximum flow rate of 3 to 5 m3/hr, while your filter pump delivers 8 to 12 m3/hr. Without a bypass, too much water passes through the heat exchanger, which prevents it from heating effectively and accelerates wear. The bypass lets you control exactly how much water flows through the heat pump.
Building a bypass in 3 steps
- Install two tees in the main pipe, spaced to match the device’s connections.
- Connect the tees via the device (the “detour”).
- Fit a ball valve on each leg: two on the device connections and one on the straight section between the tees.
By partially closing the middle valve (on the main line), you force more water through the device. Close the two outer valves and all water flows through the main line, bypassing the device entirely.
Common mistakes in pool plumbing
Avoid these problems frequently seen in DIY installations:
- Undersized suction pipe: causes cavitation in the pump (audible as a grinding noise). Always use at least the pump’s port diameter.
- Too many elbows: each elbow increases resistance. Where possible, use 45-degree elbows (half the resistance of a 90-degree elbow) or sweep bends.
- Gluing in cold or wet conditions: PVC solvent cement does not bond properly below 5 degrees Celsius or on wet surfaces. Schedule gluing work for dry weather above 10 degrees.
- No air relief: a high point in the pipe where air collects (air lock) reduces flow. Ensure pipes slope gently towards the lowest point, or install an air relief valve.
Tip
Replace two consecutive 90-degree elbows with a single sweep elbow. This halves the resistance at that point and gives you an extra 0.1 to 0.2 mWC of flow. With 6 or more elbows in the system, this makes a noticeable difference.
Insulation and frost protection for pool plumbing
In climates with freezing winters, frozen pipes mean cracked PVC and expensive repairs. Take these precautions:
- Blow out all pipes before winter shutdown with a compressor (maximum 0.5 bar).
- Fit winter plugs in the return jets and skimmer.
- Insulate any above-ground pipe runs with pipe insulation (minimum 9 mm thickness).
- Buried pipes at a depth of at least 60 cm are generally frost-safe.
For more information on connecting a heat pump to your plumbing , see the dedicated article.