It’s that time. The pool or spa filter has done a dutiful job, but it’s run its course and now must be replaced.

When doing this, you must fit it into an existing system and plumbing scheme. If it’s replaced correctly, the filter can be one of the most trouble-free components of a pool and/or spa’s circulation system.

Here, the basic steps of filter replacement are outlined.

Getting ready

Before beginning the job, you may want to pre-plumb the unit’s multi-port valve. This will save a little time in the backyard.

Once on the site, you first need to shut off all the power, since while the filter itself isn’t an electrical component, it is part of an electrically powered system. Turn everything off and, if possible, shut down the circuit breakers for safety.

Next, you must remove the old filter. (See picture 1) Saw the section of the filter influent line that includes the check valve, cutting just below the 90-degree elbows. A 24-tooth saw blade is highly effective for this task. Do the same with the backwash and return lines. Lift out the old filter and set it aside.

In preparation for the new unit, try to swivel any plumbing, such as the remaining heat sink, out of the way. (2)

Bring the new filter into place, resting the unit completely on the pad. (3) If it hangs off at all, it could vibrate, causing long-term damage. If the circulation system includes an older heater, it may need a heat sink at least 3 feet long. If so, make sure to allow for that. Position valves and the tank strap so they will be easily accessible to the service technician or homeowner for needed maintenance. Also, try to place the filter so its drain line can extend to an area with dirt or grass, rather than concrete, where the water run-out can pool.

Now it’s time to plumb the filter into the system. If the pipe coming out of the heater is 11/2-inch copper, use a compression fitting to connect it with the filter’s PVC effluent line, which should be at least 2-inch pipe. (4)

Plumb into the multiport valve with hand-tightened union connections or by bonding with an appropriate adhesive. (5) Be careful not to over-tighten. If you do, you can cause cracking.

When connecting the backwash line to the P trap, also fashion a drain line for those times when the filter just needs to be emptied. (6)

Plumb out to a tee. This can send the water to the location of your choice, such as a nearby patch of dirt.

Be sure to allow for those times when the filter will need to be serviced or replaced. At some point in the future, a technician will need to shut off the lines. If the unit sits below water level, place gate valves on both the suction and return lines. For this function, some prefer a ball or diverter valve. If above the pool, use a flap check valve between the pump and filter.

Finally, install the air-release valve and pressure gauge. (7) On cartridge and DE filters, these will be combined, with the air-relief valve screwing on the top of the tank, then the gauge on top of the valve. For sand filters, the air-relief valve still sits on the tank, but the gauge will go on the dial valve. To install, remove the plug from the top of the valve, in the case of cartridge or DE. This will leave a threaded hole for the gauge to go later. Screw it into the tank, without using lubricant. To install the gauge on top, wrap Teflon tape around the threaded area on the bottom. Move in the direction of the threads and go around two to three times. Gently screw the gauge in. Don’t over-tighten the air release valve or gauge, or the tank may crack. Let any air out of the tank.

If the unit is metallic, don’t forget to bond it. If it’s plastic, it won’t need grounding, despite the metallic strap. Since the strap is connected directly only to plastic, it doesn’t pose a hazard.

For safety’s sake, make sure to properly seat the clamp assembly and o-ring on the tank. Read the manufacturer’s instructions — some advise using a torque wrench to achieve certain specifications. An easy way to do this may be to partially tighten the clamp, then go around the perimeter of the tank with a rubber mallet or hammer handle and tap the assembly in place.

Finally, insert cartridges or charge sand and DE filters. Check that the air-release valve is open.


Plumbing Tips

Installing the plumbing to incorporate the filter into the circulation system requires a bit of precision. Take these steps to avoid leaks down the road.

1. Take the right measurements

When replacing a filter, you have to fit the unit into an existing plumbing scheme. It isn’t always easy to measure. To get the right line of pipe between elbows, connect an elbow to the open line without adhering it. With one hand, hold the next elbow where it will eventually go — say it needs to connect to the heat sink. With the other hand, measure the distance between the two elbows. Add 1 1/4 inches for each elbow or fitting that must be connected. This allows for the right amount of “stick out” to go inside the elbows or fittings for a good connection.

2. Cut straight

It may not seem important, but you’ll need a straight, level cut around the pipe. This way, it can seat precisely with the ridge that sits 1 1/4 inches into most elbows and fittings. You want it to seat all the way around if possible to prevent any gaps that could result in leaks.

3. File any burrs

Cutting pipe, whether PVC or copper, will leave a rough edge. Use plumber’s tape or emery paper to sand off the edges. Any loose particles could compromise the bond and cause leaking.
The same holds true for rough ridges manufactured inside the fittings. File them off.

4. Use proper bonders

Make sure the surface of the pipe and fittings to be bonded are completely dry.

Brush on the primer first. If the unit is going to be inspected, make sure that the primer is visible 1/2 inch beyond the connection. This makes it easy for an inspector to see it from a distance.

Not all solvents, lubricants or sealants are alike. In some cases, you need silicone, in others Teflon. Use the first letters as a clue: If the connection slips into place like an o-ring, use silicone lubricant; if it threads, use Teflon.

Apply an even coat of both primer and solvent. The amount isn’t as important as the consistency. Move quickly — the solutions dry fast.

Start with a PVC primer and solvent made for the specific plumbing. PVC and ABS require different products, so be sure to check the label first. Do not use PVC primer on any ABS lines or fittings. The solution will cause softening of the ABS over time, eventually resulting in leakage.

Once you slip the pieces into place, look for a solid bead of the solvent to form around the joint. This shows a good connection.

Before priming the pump and pressuring the filter tank, double-check that the air-release valve is open.

— R.R. and J.G.


  • Filter Replacement (Coming Soon) Watch as Bob Nichols, owner of Glendora, Calif.-based Precision Pool, and Outreach Committee chair with IPSSA, replaces a DE filter in his own backyard. Watch for tips about fitting the new unit into an existing plumbing scheme, as well as how to properly cut and glue the plumbing to prevent leaks.


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