Valves are the hands of the plumbing system. They decide where the water goes, and they decide it every time you touch them. The single most common tech error on a pad is turning the wrong valve at the wrong moment and blowing a gasket, a pump seal, or a multi-port spider. Learn the four families and their rules before you ever reach for a handle.
Before you move any valve
- Shut the pump off. Always. A closed valve against a running pump creates dead-head pressure, overheats the motor, and damages seals.
- Open the air bleed on the filter (or loosen the pump lid slightly) to release trapped pressure before breaking any union.
- Know the normal operating position of every valve on the pad. Label each handle. The next tech on the route will thank you.
Gate valves — fully open or fully closed, never in between
A gate valve has a wedge that drops across the pipe. It's built to be either all the way up (open) or all the way down (closed). Used as a throttle, the wedge erodes, the seat chews up, and you get leaks you can't fix without replacing the valve. Gate valves are cheap and reliable for shut-off duty — isolation at the main drain, at the makeup water line, at an autofill — but they are not regulators.
Ball valves — the workhorse of modern pads
A ball valve uses a hollow sphere with a bore through it. Handle in-line with the pipe is open; handle at 90 degrees is closed. Two-way ball valves shut off a line. Three-way diverter valves (the black plastic “Jandy-style” valves you see everywhere in Florida) split or combine flow between two paths — main drain and skimmer suction, spa return and pool return, heater bypass. They can be set anywhere between fully open and fully closed without damage, which is what makes them the default control valve on a modern pad.
- Expect O-rings to need replacement every 3–5 years on sun-exposed valves.
- A stiff handle usually means a dry O-ring. A quick lube of silicone grease before it leaks beats replacing the valve.
- Mark the handle position with a permanent marker or a manufacturer's rotation stop so you can confirm it's back where it belongs after service.
Check valves — one-way traffic
A check valve is a spring-loaded gate that allows flow in one direction and slams shut against flow in the other. Required on heater inlets (so hot water can't back up into the filter), on chemical feeder lines (so pool water doesn't siphon backward into the chemical tank), and anywhere code requires backflow prevention.
- The arrow on the body tells you which way it should flow. Install it backwards and the system will fight you forever.
- Debris trapped in the spring is the #1 failure mode. A check valve that won't seat lets pump prime drain back to the pool overnight.
- On salt-chlorine systems, place a check valve on the cell's downstream side to keep salty return water from migrating back to the heater when the pump is off.
Butterfly valves — commercial and larger diameters
A butterfly valve is a disk on a shaft that rotates inside a ring. Open in-line, closed at 90 degrees, like a ball valve. You'll see them on 3" and larger commercial plumbing where ball valves get prohibitively expensive. They can be motor-actuated for automation on large systems. Expect to replace the EPDM seat every 5–10 years; a butterfly that won't fully close almost always needs a new seat, not a new valve.
Hard rule: before you crack a union, put your hand on the pump switch first. A valve surprise at 3,000 rpm is a hospital visit.