Medium Head

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These are faster operating than screw actuated valves, due to a geared drive mechanism, so are more convenient to use if a number of valves have to be operated.
Having a lower mechanical advantage, they will be harder to open if seized, as may be the case after a lengthy period of disuse.  Each valve is equipped with a screw-jack, used with a spanner, to break a stubborn seal.  The jack is located at the top of the valve, within convenient reach.
A ratchet pawl allows the valve to be locked in any partly-open position.
Gear teeth are of precision machined steel.  The shaft carrying the handwheel and pinion is mounted in ball bearings.  Extension frames are available, to increase the height of the handwheel in deep installations.

Corrosion Resistance.  Normal construction is of mild steel, hot dip galvanised.  Stainless Steel, in grades 304L or 316L, may also be specified.

Sealing Method.  A flat steel door slides vertically within the side frames, and is inclined at a slight angle, as seen in the illustration.  A rubber sealing ring, which is riveted and glued into a recess in the body of the valve, is inclined at the same angle as the door.  The door and seal come together with a wedging action, as the door is lowered.

Installation.  These valves are normally grouted  into pipes or headwall structures.  The body spigot has attached lugs, which will lock into the grout and also assist with aligning the valve in the pipe opening.  The spigot and lugs fit, with a slight clearance, within Class 2 concrete pipe.

Sizes and Pressure Rating
Standard sizes fit Class 2 concrete pipes, from 600mm to 1200mm.
Pressure ratings are given, in the table below, as on-seating and off-seating pressure.  'Off-seating' is pressure applied to the valve from the side of the grouted pipe.

Nominal valve size (mm) and maximum on-seating /off-seating pressure, expressed in metres head.

Nominal Diameter







Pressure On/Off