Presair

Presair air switches and pressure switches for spas and pools

Presair switches are the small pneumatic components that sit behind the air buttons on a spa or pool control panel. Instead of carrying mains voltage to a button the bather touches, the button pushes a column of air down a length of flexible tubing to a switch mounted inside the dry equipment bay, where a diaphragm moves the electrical contacts. The water and the electricity never meet, which is why this arrangement has been used in wet environments for decades. Here you will find momentary and latching air switches in SPDT and DPDT configurations, together with a low-pressure water pressure switch for safety interlock duty.

What an air switch does in a control circuit

An air switch is a mechanical contact set operated by pressure rather than by a finger. A short puff of air from the panel button lifts a diaphragm, the diaphragm moves the actuator and the contacts change state. Because the actuating medium is air, the switch itself can be placed wherever it is convenient to wire it, and the button on the shell can be positioned purely for the bather’s comfort.

Air switches wear in predictable ways. The diaphragm hardens and loses its spring, the tubing perishes or becomes waterlogged, and the contacts pit from switching inductive loads such as pump motors and blowers. The usual symptoms are a button that needs several firm presses, a pump that will not switch off, or a circuit that chatters. In most cases the switch is replaced rather than repaired, and the tubing is renewed at the same time.

Momentary, latching and the contact configurations

Getting these two characteristics right matters more than anything else when ordering a replacement, because a visually identical body can behave completely differently in circuit.

• Momentary — the contacts change state only for as long as air pressure is applied and return as soon as the button is released. The TVM111A is a momentary SPDT switch, typically used where a pack or timer board does the actual latching and only needs a pulse.
• Latching — each press alternates the switch between its two positions, so one press runs the pump and the next stops it. The TVA111A and TVA211B are latching types.
• SPST — single pole, single throw: one circuit, simply made or broken. The TNP411R pressure switch uses this arrangement.
• SPDT — single pole, double throw: one common terminal with a normally open and a normally closed contact, so one load can be switched or two can be alternated.
• DPDT — double pole, double throw: two independent changeover contact sets operated together, used where two circuits must be switched at once, such as a two-speed pump.

Spout position, current rating and mounting

The spout is the barbed nipple that accepts the air tubing. On the TVA111A and TVA211B it sits in the centre of the switch body, which suits installations where the tube runs straight up to the switch; side-spout variants exist for tight bays where the tube must turn. Check which direction the existing tube leaves the switch before ordering, as a centre spout in a shallow compartment may force an awkward bend.

The 21 A rating quoted on these models refers to the contact current capability, and should be matched to or exceed the rating of the switch being replaced. The TNP411R-1.8PR is a different device: a pressure switch with a 1.8 psi closing point, intended to sense that water is actually moving before a heater is allowed to energise. Its setting is fixed, so it must be matched to the pressure point specified for the heater or control pack rather than chosen by appearance.

When identifying a replacement, note the model number stamped on the body, count the terminals, confirm whether the action is momentary or latching, and measure the panel cut-out and the thickness of the material the switch is clamped through. Photographing the existing wiring before disconnecting it saves a great deal of time later.

Presair at PoolParthub.com

Here we list the pneumatic switches most often needed for spa and pool control circuits: momentary and latching air switches in SPDT and DPDT form, centre-spout versions for straight tube runs, and a low-pressure SPST pressure switch for heater interlock duty. Each is listed with its model reference so it can be cross-checked against the part already fitted.

These are small components that stop an entire system working when they fail, which is why they are worth keeping accessible. If the model number on the existing switch is unreadable, describing the action, the number of terminals and the spout position is usually enough to narrow the choice down to a single item.