Featured Story – Application of gate valves in potable water distribution systems

^ Foremost gate valve type is one with a non-rising stem

Article By Naveen Goveas
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A gate valve is not used for throttling flow or for frequent operation. Either will cause excessive wear on the seating edges of the discs and guides. Irregular operation may cause the valve to freeze in one position or become difficult to operate. Where the water carries small amounts of sand or silt, the valve seats may fill with deposited material unless operated at regular intervals to keep the valve seat clear. These are mostly resilient seated gate valves. They are low in head loss and offer minimum internal restriction due to full diameter passage when fully open.

For 12-inch and smaller lines, gate valves are the most common type of valve used in underground applications in water infrastructure. Gate valves come in many different sizes depending on the water lines they are being installed to. Gate valves are available with bell, spigot, flanged, mechanical joint or slip-on ends. The most often used types are with flanged and spigot ends. The gate valve’s desirable position is either fully open or closed. It is used to isolate the water flow in the water supply line. The valve wrench or key is used through the valve box shaft to turn the valve on and off.

The Spigot end gate vales used for buried installations. The valve shall be supplied with water tight gland to have 100 per cent water tightness between neck of the valve body and PVC pipe. Ideally this type of installations is used for depth up to 1.5m. If lower, then standard valve chamber of concrete block shall be constructed. The valve must be wrapped properly using moulding putty and self-adhesive bituminous wrap as per manufacturer / authority recommendations. 

Spigot gate valves operated using an extension and a t-key arrangement. The very important advantage is easy installation in a new line or any replacement of old valve. These are very easy to operate with less torque.

Flanged gate valves mostly used as wash out valves on pipe lines 450mm diameter and below. However, they can be also used as line valves when they are installed inside a concreate chamber. Valves shall be supplied with stem cap for valves installed underground and with hand wheel for valves installed above ground.