Submersible Pumps Install Guide
A submersible pump sits down in the water it is pumping, inside a tank, a sump or a pit, and lifts that water up a discharge line to a point above ground. Installing one well comes down to three things: pick a pump that matches your worst case water, set the float so the pump shuts off before it runs dry, and put a non return valve and a union on the discharge so you can lift the pump out later without cutting pipe.
Everything below is how we do it on jobs around Waihi and Thames. Read your pump manual as well. It wins any argument with this page.
The short answer
Match the pump to the application. Clean water, dirty water and sewage are three different pumps.
Float switch setup is the most common failure point. Give it clear space to swing.
Non return valve close to the pump, inside the pit but still reachable for cleaning.
No cable joins below water. Run the cable up the discharge pipe and form a drip loop.
Float test at commissioning. Watch it go through a full cycle before you walk away.
Which submersible pump do I need?
One of the biggest mistakes in submersible installs is using the wrong pump type. A clean water submersible pumped through silt or solids will block and overheat, and sooner or later it burns out. A vortex or solids handling pump used for clean water service will work, at the cost of efficiency and head.
Pick the pump that matches your worst case water, not your average water.
Vertical lift and total head
Nearly every submersible install lifts water vertically from the pit or tank to a discharge point above ground. The pump must be rated for the total head, which is the vertical lift plus friction losses in the line. Head varies a lot in submersibles. All the details are on the product pages.
Clean water house supply
For rainwater tanks catching clean drainage and little debris or solids. Designed to be installed inside your tank out of sight and practically silent.
Try the DAB E.SYDIVER or the Grundfos SBA.
Dewatering pumps
For sump pits that catch silt, leaf litter, sand and soft solids. The vortex impeller has no narrow clearances, so debris passes through rather than blocking. Check the solids rating on the model you pick, it differs across the range. Dewatering trenches, pits and flood response work also sits here.
The Davey vortex line has you covered, smallest to largest: D15VA, D40VA, D75VA.
High head dewatering
Where you need to pump to a higher elevation and still move a small amount of solids, reach for the Davey D23AB. Pumping up to 22.5m and moving solids up to 1mm in diameter.
We often install these in the second chamber of septic systems, pumping out to the irrigation field.
Sewage and grinder pumps
Raw sewage needs a pump built for it. These have larger passage impellers and are rated for solids up to a stated size. We like the Grundfos Unilift AP35B or AP50B. See the sewage pump range.
Grinder pumps suit sewage with high solids, or where the discharge runs uphill or through small bore pipe. The grinder cuts solids before pumping, so the discharge line can be smaller than a non grinder sewage pump. The Grundfos APG40 is our pick.
Wipes
Wipes are the number one cause of blocked pumps. Nothing on the market handles them reliably, and even a grinder will rag up on them eventually. Our advice is to never flush wipes.
Still deciding? The full submersible pump range, the dewatering pumps and the house pumps are all online with head and flow figures on each product page.
What do I need before I start?
- Read the manufacturer manual.
- Unplug the pump. If it is hard wired, an electrician isolates and locks off at the switchboard before anyone touches it.
- Turn off valves and taps.
- Put together a list of parts you are going to require, not a hardware store detour list.
- Measure twice, cut once.
Fittings, valves, unions and cable ties are all in pump parts and accessories. Getting the whole list in one go is the difference between a two hour job and a two day job.
Electrical work is an electrician's job
Everything on this page assumes a plug in pump going into an existing outdoor rated, RCD protected socket. That part you can do yourself.
Anything else is prescribed electrical work in New Zealand and has to be done and certified by a registered electrician. That covers hard wiring a pump, fitting or moving an isolator, running a new circuit or outlet, changing a capacitor, and repairing, shortening or joining a pump power cord. Do not open the pump body, and never work on a circuit that is still live.
If the outlet is not RCD protected, get an electrician to fix that before the pump goes in the water.
Where should the pump sit in the pit or tank?
Off the bottom
Sit the pump on a brick, a paver, or a purpose made pump stand. Direct contact with the floor pulls sediment straight into the intake. A few centimetres of clearance underneath makes a real difference.
Clearance for float swing
If the pump has a float, the float needs clear space to swing through its full arc without hitting the wall, the pump body, the cable, or any incoming pipework. This is the single most common failure point on a submersible install, and it costs nothing to get right at the start.
How do I plumb the discharge line?
Sized to spec
Most submersibles have a 25mm to 50mm threaded discharge. Use the same size or larger for the run. Going smaller costs you flow, and less flow past the motor means less cooling, so the pump runs hotter. In some septic situations a smaller line will also clog.
Non return valve
Most house pressure pumps have a non return valve built in, but check yours before you fit a second one. For fixed dewatering pumps, fit a non return valve inside the pit but somewhere accessible, as these may need to be cleaned from time to time. With no non return, water sitting in the pipe flows back into the pit when the pump turns off, which leads to the pump cycling on and off.
Union on the discharge
A union or camlock fitting on the discharge line above water makes service easy. You can lift the pump out for maintenance without cutting and rejoining pipe.
Plumbing rules that stop leaks and callbacks
No dry running
Ensure that the float turns the pump off before it runs dry. Dry running damages seals, melts internal components, causes leaks, and shortens the life of the pump. It does not take long to do the damage.
Every manufacturer we deal with excludes dry running damage from warranty. Check your manual for the exact wording.
Thread tape or sealant on every threaded join
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. Tape on those stops the seal seating and causes the leak you were trying to avoid.
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. What matters is the direction: the tape has to run the same way the fitting screws in, so tightening pulls it 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 cures to a firm seal that holds up better over time than tape does, especially when there is movement or water hammer in the system. Check the label is rated for potable water before you use it on drinking water lines.
Support the pipework and the pump
A submersible needs to sit square and stable on its landing surface so it does not walk under vibration. Do not bolt it down. You want to be able to lift it straight out on its rope for service, which is the whole point of the union above water. If a pump keeps shifting, fix the landing surface or fit a proper pump stand rather than fastening the pump to the floor. Surface mounted pumps are different, and those do get bolted to their base.
The pump weight should never hang off the plumbing. The discharge line should be supported with brackets or clips so it carries its own weight, not pulling on the pump body.
Why do submersible pumps fail electrically?
Submersibles are built to live under water, within the depth and duty their rating allows, but the old line that water and electricity do not mix still applies.
The three places submersibles fail electrically are the capacitor, the float switch, and the power cord at the entry point on the pump body.
All three are repairs, not owner jobs. A capacitor holds a charge after the power is off, and a cord repair has to restore the seal at the cable gland or the motor floods next time it goes under. Unplug the pump, pull it out, and bring it to us or to an electrician rather than opening it up in the pit.
Pumps that last
Pumps that sit in one place for years, like tank submersibles and permanent sump pumps, rarely have electrical problems. They go in once, the cable never moves, and the motor stays under water.
Pumps that do not
Dewatering pumps that get moved between sites, lifted by the cable, dropped on rough ground, and run dry on a regular basis do not last. That kind of handling cracks the cable jacket, works the cord loose where it enters the pump body, and lets water reach the motor over time.
If you are buying for hard duty use, lift it by the handle or attach a rope, and try not to run it for extended periods with the motor out of the water.
Surge protection
Voltage spikes are a common cause of dead controllers on pumps. Some pump systems also include delicate electronics, so although it is not usually a warranty requirement, a surge protector is cheap insurance for a brand new piece of kit. We sell them online, for example the Puretec PC-SURGE 240V surge protector, and most hardware and electrical retailers carry them too.
What pressure should a submersible house pump run at?
Do not run pressure above 500 kPa (72 psi) into the house without a pressure limiting valve in place. That 500 kPa figure is the Building Code limit at the fixtures, not a rule of thumb. 300 to 400 kPa is great pressure for most households. Most domestic house pumps are set up so they will not deliver more than that, and plenty of houses already have a pressure limiting valve fitted somewhere. Do not assume yours has one. Put a gauge on it and check.
Pressure tanks
Dewatering pumps do not need a pressure tank. For a submersible pressure pump that supplies your house, a pressure tank is beneficial. We recommend installing at least an 18L Davey Supercell on any pressure system running off a pressure switch. Smart controllers like the Torrium2 and the PM PLUS will run without a tank, but a tank still cuts cycling on small draws and takes load off the pump. Bigger is better.
Pressure settings
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 Grundfos 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 commission a submersible pump?
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Prep the tank or pit
Confirm the pit or tank is reasonably clean of debris, the inlet is positioned away from the float, and the pump landing surface (brick, paver, stand) is level and stable.
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Set the float switch
Position the cord clip at the estimated right height. Test the swing dry: lift the float through its full arc and confirm it does not hit anything.
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Position the pump
Lower the pump in on its lifting rope or handle. Sit it on the landing surface.
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Connect the discharge line
Fit the discharge pipe with the non return valve if required, and a union or quick disconnect above water.
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Set the cable
Run the cable up the discharge pipe, cable tie it loosely every metre or so, and form the drip loop above the pit.
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Energise and test the float
Plug the pump into an RCD protected outlet and allow it to go through a full emptying cycle by adding water or emptying what is already there. Stay out of the water while it is live. Ensure the float switch moves unobstructed. You may not be able to do this on a full large tank or sump.
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Leak check above water
Go over every join you can see and touch. A weep at commissioning becomes a flood at year two.
Talk to us
Stuck part way through an install? Call us. A real person answers the phone. A photo and a question by email works just as well, and it is often faster than describing a pit over the phone.
Or come and see us: 65 Kenny Street, Waihi, Monday to Friday 8 to 5. 74 Kopu Road, Kopu, Thames, Monday to Friday 8 to 3.
