Sealing relies on pressure differential between
inlet and outlet. The door has resilient rubber seals, which contact
stainless seats in the branch pipes.
Diverters may be used instead of two gate valves, to reduce change-over
time between lines, although this time advantage will be lost if excessive
time is required to equalise pressure.
6mm material, in either mild steel, galvanised after fabrication, or
stainless steel grades 304L or 316L.
Flanges may be fitted, as above, or plain spigots provided
for welding or grouting.
The cost of flanges is not included
in the standard price. For choice of flanges, click
here. Details of modified Table D flanges are given with valve
dimensions, see Dimensions.
Mixed inlet and outlet sizes may be specified when ordering and,
if welding the valve to a pipeline, spigots to match an existing pipe
diameter may be ordered.
Seals of various thickness and hardness are used, to suit the
maximum operating head to be encountered.
Please advise maximum head, when ordering.
RESISTANCE. Hot dip
galvanising is the preferred finish for all valves within the standard
size range. If larger valves
are made to order, it is necessary to check the availability of
Coal-tar and other epoxies may be used as
alternatives to galvanising, or as additional protection after
GEAR ACTUATORS. Various
types of gear and ratchet drive have been fitted to these valves, for
better control of the door. Our
Technical Services Dept. can advise on the options available.
WARNING. Valves equipped with a hand lever. Do not change the flap position while a flow exists through the
valve. The flap will 'catch' in the flow and snap over rapidly,
possibly causing injury and water-hammer.
WATER-HAMMER. In some
situations a pressure surge, of perhaps ten times the normal line
pressure, can occur, when a flap is closed suddenly while a flow still
exists through a valve. This could be sufficient to rupture pipes or
fittings. This requires careful consideration when
designing any system in which it is proposed to use a diverter valve.
It is usually necessary to equalise pressure between inlet and the
closed line, before operating the valve.
This can be achieved by a bypass line and stop valve, preferably fitted
at manufacture. The size of a
bypass will depend on the volume of water to be shifted. This
feature is an optional extra, size required needs to be advised when
Standard Valve Sizes.
Nominal inlet bore (mm).