Uses of the Knife Gate Valve
Light, simple, and easy to install, operate and maintain, the knife gate valve that professionals are familiar with is not well known by individuals. A knife gate valve can be considered whenever a shut-off valve must be created on a pressure or wastewater network. Its PVC body allows easy installation on any supply and discharge network made of PVC pressure pipe, but also in pools and swimming pools when pressure with earth or sand may be present. We will talk to you about it right now in this article!
Knife gate valve: how it works
The knife gate valve is basically a slide valve (or gate valve). The flap is opened by simply raising the stem, and the liquid flows through the valve, or by lowering the stem, the flap descends into the body like a guillotine blade. The flap’s lowering and raising are done by a rod equipped with a handle or a handwheel.
For this purpose, the knife gate valve is designed as a narrow body (no rotating element requiring volume) into which the flap descends, and connecting sleeves are attached on both sides.
Note: the drop of the flap is not at all intended to be proportional. It is rather of the type “all or nothing”. That is why the knife gate valve is instead a stop valve than a control valve.
Uses of the knife gate valve
Because the shut-off system (the flap in direct descent) is simple or even simplistic, without bearing or rotation axis, the knife gate valve is perfectly adapted to
for dirty water (pool sand, earth in a pond or a pool, sewage, rainwater drainage, grey and black water…) because the flap’s descent system is not affected by dirt, nor by granulometry. In case of clogging, dismantling, maintenance, and reassembly are simple, quick, and easy;
to relatively pressurized water since the flap is guided in the body of the valve without deformation under the pressure of a liquid;
Sensitive products because the valve body is usually made of PVC with a conventional steel or stainless steel flap that is insensitive to most chemicals, fuels, chlorinated water, etc., and has no internal mechanism that could degrade or create sparks.
Light with its diameter, the knife gate valve can be mounted on almost all pipes, both rigid (PVC, PVC pressure…) and flexible (corrugated tube), with a diameter greater than or equal to 50 mm.
The different diameters available correspond to the main uses of the knife gate valve: 50, 63, 75, 90, 110, 160, 200, 250, and 315 mm.
Good to know: the guillotine valve has a system of descent of the shutter by a handle; it is almost impossible to motorize it for remote control. However, installing a pull cord and a cable on the handle makes it possible to open remotely to empty the tank without entering the room (police valve).
Criteria for choosing a knife gate valve
The choice of a knife gate valve is made consecutively, according to the following:
the diameter of the pipe on which it is to be installed (from 50 mm to 315 mm);
the pressure of the liquid flowing through the pipe;
the material of the knife gate (steel or stainless steel).
Most PVC knife gate valves can operate at a pressure of 2.5 to 3.5 bar when their diameter is limited (50 mm to 63 mm). Still, you should limit yourself to the current atmospheric pressure (1 bar) for larger pipe diameters.
Good to know: before choosing where to install the knife gate valve, it is necessary to foresee that the valve will have to remain accessible for its maneuvering but also for disassembly (it is foreseen for that) to clean and maintain it, especially in the presence of loaded water.
Installation of a knife gate valve
It is sufficient to isolate the circuit and then uncouple the sleeves from the valve body to dismantle a knife gate valve, especially for cleaning.
Generally, the assembly is made of 4 or 6 screws (or more, depending on the diameter) and sealed by two gaskets that are easily replaced.
Please note: a PVC knife gate valve should be chosen for supply and discharge pipes made of rigid or corrugated PVC. It is easy to assemble by neoprene gluing for rigid PVC or clamps for corrugated PVC.