Flooded Suction Installation Guide

What is a flooded suction pump setup?

The pump inlet must sit below the level of water in the water source. That puts positive pressure on the pump inlet, meaning it does not have to suck. Pumps in this category are more quiet and energy efficient than their suction lift counterparts.

It also means the pump primes itself. Open the valves and gravity fills the suction line and the wet end of the pump for you, which is why a flooded suction install does not need a foot valve holding the prime the way a suction lift install does.

If your tank sits below the pump, or the pump has to lift water up out of a bore or a creek, that is a suction lift install and the rules are different. Everything below assumes the tank outlet is above the pump inlet.

Before you start

• Read the manufacturer manual
• Isolate electrical at the switchboard or unplug everything
• Turn off valves (taps)
• Put together a list of parts you are going to require, not a hardware store detour list
• Measure twice, cut once

Electrical

Surge protection

Voltage spikes are a common cause of dead controllers on pumps. Some pump systems also include delicate electronics, so a surge protector is cheap insurance for your brand new piece of kit. No manufacturer makes you fit one, but surge and lightning damage is generally not covered by warranty either, which is the point. We sell surge protectors in our online store, but your local Bunnings or Mitre 10 will stock these cheap pieces of kit.

Water and electricity do not mix

Anything running outdoors should be on an RCD protected circuit. If you do not know whether your pump outlet is, ask your electrician before you commission the pump.

Most pumps are designed for at least a little moisture. To extend the life of your new piece of equipment, it is always best practice to have the system well protected by a pump cover or installed out of the elements. Pumps that are exposed to the elements will more regularly have motor and controller issues, and often need replacement motor bearings more regularly than those that are well protected.

Plumbing that applies to every install

Use thread tape or thread sealant on threaded joins, but never on O ring or washer sealed joins

Thread tape (PTFE) or a liquid thread sealant, and sometimes both, goes on any threaded join. The exception is joins that seal on an O ring or a flat washer, like union nuts and camlocks, which get nothing at all, because tape there stops the seal seating and causes the leak it was meant to prevent. Hose tails are their own case: they take thread tape on one side only. The easiest way to remember how to apply thread tape is to hold the fitting in your left hand and wrap the tape around the thread by rolling it away from you, six to seven revolutions. The direction matters: the tape has to go on clockwise as you look at the open end of the male thread, so screwing the fitting in pulls the tape tighter instead of unwinding it. Try not to get tape on the first couple of threads that slot into the female fitting, or you will end up cross threading or fighting alignment.

When to use Loctite 5331 instead of tape

Thread tape has weaknesses compared to a liquid sealant. If you tighten a thread too far and have to back off, the tape often leaks and you have to redo the join. For plastic and PVC connections we often use a liquid sealant like Loctite 5331 instead. Two benefits. You can adjust the thread as you fit the pump without losing the seal. And 5331 sets firm, which holds the thread together far better over time, especially when there is movement or water hammer in the system.

The exception: o-rings and gaskets

There is one place you do not use thread tape or sealant: when the fitting has an o-ring or gasket to seal it. Things like unions where the pressure controller meets the pump sometimes have an o-ring doing the seal. These connections do not want tape or sealant. Adding it usually causes a leak.

Short video example here.

No dry running

Support the pipework and the pump

The pump should be securely bolted or screwed to whatever it is sitting on. That stops the pump walking under vibration, and it stops vibration travelling out through the pipework. The pump weight should never hang off the plumbing. The plumbing itself should be supported with brackets or clips so the suction and discharge lines are carrying their own weight, not pulling on the pump body.

Avoid air locks

On the delivery side, the line from the pump to the highest fixture should rise consistently. No traps. House pumps rarely run into air lock issues on the delivery side.

On the suction side, air locks cause real problems. Avoid any section of pipe where air can collect. A steady, constant gradient beats sharp turns or pipe runs that rise then drop sharply.

Where should the pump go?

Below the level of water in storage

This is the one that makes it a flooded suction install. The pump inlet sits below the water level in the tank so the pump never has to lift water to get started.

Stable, level base

A concrete pad is best, but you can also level the ground and place a couple of large pavers to mount the pump and pump cover to. Bare ground is not ideal as it can lead to additional moisture, water ingress and insect damage. Keep the base level not only for looks, but to ensure plumbing connections are easier to make.

Under cover

You have made a big investment in your new pump, so install it in a pump shed, a lean to, or a weatherproof enclosure.

Although most pumps are reasonably weather proof, they do not like rain or sun. The controller especially. Direct UV degrades plastics, and rain ingress over time will reach the electronics no matter what the IP rating claims. If installing outdoors, purchase one of our Davey pump covers.

Service clearance and ventilation

Leave some clear space above the pump for service access, and at least 200 mm behind the motor fan for airflow, or whatever clearance your manual asks for. Do not install in a sealed cupboard with no airflow, as pump motors generate heat and need to be vented.

Suction line, from tank to pump

Sized to spec

Most house pumps want 25 mm or 32 mm suction line. Check the manual for your specific pump. Going smaller than spec costs you flow and can cavitate the pump. Going bigger is fine.

Rule of thumb here is the same size suction line internal diameter as the inlet size on the pump. 25 mm inlet size, use pipework with a 25 mm internal diameter.

Watch the trap here. Poly pipe is sold by outside diameter, so 25 mm poly is only around 20 mm on the inside and it will choke a 25 mm inlet. To get 25 mm of bore you usually need 32 mm poly. Ring us if you are not sure what your pipe measures.

Short and direct

Every metre of pipe adds friction on the suction side. Keep the run as short as the layout allows. Talk to us if your suction line is going to be over 20 m long.

No high points

Avoid sharp lifts and drops on the suction line where possible. These can lead to air locks which will cause the pump to cavitate or even run dry.

Filtration on the suction side

If you do decide to install any type of filtration on the suction side of the pump, you need to be diligent in cleaning out the filtration, as blocked screens and filtration can damage your pump through cavitation or running dry.

For a rain collection tank, it is always best to stop the debris getting into the tank in the first place, using filters on downpipes or a first flush system. We also recommend a floating suction system inside the tank. Give us a call and we will sort one out for you. It is one of the cheapest insurance policies on the whole install.

A mesh strainer on the tank outlet stops leaves, grit and silt from reaching the pump impeller.

Non return or check valve

If the pump is a variable speed pump or has a pressure controller, a non return is usually built in. Check the manual for your model rather than assuming it. If the pump is running on a pressure switch, the non return can go anywhere before the switch. The pressure switch always sits downstream of it. That way the house side holds its pressure instead of draining back into the tank when the pump stops. That is not the same thing as a foot valve. It sits at the pump, not down in the tank, and a flooded suction install still does not need a foot valve.

Discharge line, from pump to house

Pressure switch or controller

Electronic pressure controllers and variable speed pumps (Davey EvoDrive, DAB Esybox, and similar) include the pressure logic built in, and most of them carry dry run and rapid cycling protection as well. Check what your model actually has, and do not treat it as a licence to skip priming. Dry run protection cuts the pump off after it has already been running dry. You do not require a pressure tank with these, though one can still help.

Discharge side valve

Fit a valve (tap) on the discharge side so the house can be isolated from the pump without draining the system for servicing, but also for helping diagnose issues like identifying where leaks are in the system.

Do I need a pressure tank?

Most modern pump setups do not need an extra pressure tank. The variable speed pumps we sell, like the Davey EvoDrive and the DAB Esybox, have pressure tanks built in. And when you use a flow and pressure controller like the Torrium or the PM Start, the controller does most of the work a pressure tank would otherwise do in smoothing out rapid cycling.

That said, a pressure tank has real benefits and can be added to any pressure system. It cuts the number of starts the pump makes, which is where most of the wear on a motor and a controller comes from. The tank delivers stored water first, so the pump does not have to fire up for every small draw. Only part of a pressure tank's volume is usable drawdown, roughly a fifth on typical 300 to 400 kPa settings, so you do not need a huge tank to make a difference. It also reduces water hammer and vibration through the plumbing, because there is an air cushion in the tank to expand and contract as pressure shifts.

A pressure switch setup must have a pressure vessel. Without one the switch has nothing to hold the pressure between cut in and cut out, so the pump hunts on and off every time a tap cracks open. We fit an 18L Davey Supercell as the sensible default on a switch, and it is worth having on a controller too. A bigger tank holds more, but talk to us before you go much larger on a smart controller setup, as those are tuned to run with a small tank or none at all.

What pressure should the pump be set to?

Most house pumps are set up so they will not deliver dangerous pressure into the house. Plenty of houses on town supply have a pressure limiting valve fitted somewhere, but tank fed rural houses often do not, so check yours rather than assuming it is there. As a rule, do not run pressure above 500 kPa (72 psi) into the house without a pressure limiting valve in place. 300 to 400 kPa is great pressure for most households.

Some pressure controllers, and most smart variable speed pumps, let you adjust the setpoint. We recommend using a pressure controller with a built in pressure gauge like the PM Plus, or fitting a separate pressure gauge in the system so you can see what the pump is doing.

Pressure limiting valve where the supply needs it

Separate from your downstream pressure setting: if the incoming supply itself can exceed the rating of any component, whether that is the pump, the filtration housings or the downstream pipework, fit a pressure limiting valve upstream of those components. For filtration housings specifically, anything above 500 kPa upstream needs a pressure limiting valve.

How do I start a flooded suction pump for the first time?

Work through these in order. The pump stays switched off and unplugged, or isolated at the switchboard, for steps 1 to 3. Do not skip the bleed step, and do not power the pump up until water is coming through it.

1. Check the tank water level

   Confirm the tank or other water source has enough water that the outlet is fully submerged. If the tank is low, fill it before you start.

2. Open the suction valve and bleed the pump

   With the pump still isolated, open the suction valve and tank valve. Water should fill the suction line and the pump body by gravity. At the same time, most pumps have a priming or bleed plug on the stainless or plastic wet end. Open this and allow water to flow out of it until there are no more air bubbles, then close it. If the pump has a high point that traps air, crack a fitting at the high point to bleed it. Only ever do this with the pump off and the system unpressurised.

3. Open the discharge and flush downstream

   Open the discharge valve. Open a tap at the house to allow air and new water to travel through the system.

4. Energise the pump

   Power on the pump. The pump should start and start pumping water through the system to the open tap at the house.

5. Watch the pressure cycle

   Close the valve on the outlet of the pump. Pressure should rise to the cut out setting. The pump should stop within 30 seconds of reaching its max pressure. Open the valve again. Pressure will fall and the pump should restart again. If it does not shut off, open the valve straight away and switch the pump off. Running a pump against a closed valve heats the water in the pump body and will cook the seal, and it means the pressure switch or controller needs looking at before you go any further.

6. Leak check

   Turn the tap off at the house. If no water is being used, the pump should pump up to pressure and turn off. Spend some time going over every new connection point and piece of pipework to ensure there are no leaks. Even a small leak will lead to the pump cycling on and off and early wear.

When to call someone

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