Pool Plumbing Fittings

What size is my pool plumbed in?

Almost certainly 1-1/2 in. or 2 in., and those two are most of this page. Measure the outside of the pipe rather than the inside, because PVC is named by its nominal bore and not by what a tape reads: nominal 1-1/2 in. pipe measures about 1.9 in. across the outside and 2 in. pipe about 2.375. That catches people out constantly. Older pools and above ground equipment turn up in 1-1/4 in. and 3/4 in., and commercial work goes up from 2.

Slip or threaded?

Slip where it will never come apart, threaded where it might. A slip fitting is solvent welded, which chemically fuses the pipe and the socket into one piece: it is stronger than the pipe and it is permanent. Threaded joints can be undone, which is what you want at equipment, but every thread is a potential leak and plastic threads crack if overtightened. The rule most builders follow is to use as few threaded joints as possible and to put unions where you will actually need to break the line.

What is a union for?

Getting equipment back out without a saw. A union is two halves and a nut with a seal between them, so a pump or a filter can be unbolted and lifted away leaving the pipework intact. Without one, replacing a pump means cutting the pipe and gluing in couplings, which shortens the run a little each time until nothing lines up. Unions either side of a pump and either side of a heater are the cheapest thing you will ever be grateful for.

Is schedule 40 the right pipe?

For almost all residential pool work, yes, and it is what the fittings here are made to. Schedule refers to wall thickness rather than diameter, so schedule 40 and schedule 80 of the same nominal size have the same outside dimension and fit the same sockets, with 80 being thicker walled and rated higher. Pools rarely need 80 outside of commercial and suction line work. What matters more is that everything you glue together is actually PVC and rated for pressure, not drain pipe.