A pressure-reducing valve takes the high, changing pressure of the water main and feeds it out at a lower, steady pressure. Use the buttons to look inside and follow the water past the poppet, where the spring and diaphragm decide how far it opens.
A pressure-reducing valve is a fitting that takes water at a high, often varying pressure from the mains and delivers it at a lower, constant pressure. It is common on the supply to a tap, a whole house, or an appliance, where too much pressure would hammer the pipework, waste water and wear out seals.
From the outside it is just a lump of brass with a pipe in and a pipe out and a screw on top. Everything that matters is hidden inside, so opening the body reveals the poppet, seat, diaphragm and spring that work together to hold the outlet pressure steady.
Water arrives from the mains at a high, changing pressure. It flows in through the inlet and up to the poppet, which sits in the way of the flow rather than blocking it completely.
The poppet and the seat form a gap. Because the water has to squeeze through this narrow opening, its pressure drops on the way past. How wide the gap is at any moment decides how much pressure is let through.
The outlet pressure acts on the underside of the diaphragm, which is joined to the poppet by a stem. If the outlet pressure rises above the set value, it pushes the diaphragm up — and the poppet with it.
As the diaphragm moves up, it compresses the spring above it. The spring pushes back down, and the two forces settle into a balance. The poppet then sits at just the right opening to hold the outlet at the set pressure.
The adjustment screw at the top presses on the spring. Turning it in increases the spring force so the valve holds a higher outlet pressure; turning it out lowers the target. The valve keeps returning to this balance as the flow changes.
It takes water at a high, changing mains pressure and feeds it out at a lower, steady pressure. It does this by throttling the flow, not by blocking it, so taps and appliances downstream see a safe, constant supply.
The poppet sits close to the seat, so the water has to squeeze through a narrow gap. That restriction drops the pressure, and the spring and diaphragm decide just how far the poppet opens to hold the outlet at the set value.
It is self-adjusting. If more water is drawn the outlet pressure dips, the diaphragm moves down, the poppet opens a little more, and the pressure comes back up. If the pressure rises, the diaphragm lifts and the poppet closes slightly.
The screw sets how hard the spring presses on the diaphragm. Tightening it raises the spring force and the target outlet pressure; loosening it lowers both.
Yes. With no flow the outlet pressure pushes the diaphragm up until the spring force balances it, and the poppet closes against the seat so the downstream pressure holds at the set value.