Batescrew Extreme Head Valves
Design

  Click here for Important NOTES on SYSTEM DESIGN.

CONSTRUCTION  These valves are of heavily reinforced fabricated construction, made from either mild steel, epoxy coated internally and externally, or stainless steel.
Bodies are fully enclosed and, in the case of the three metre diameter valve, extend in height to 8.1 metres, allowing removal of the top cover for maintenance, without overflow of water from a full dam.  Higher bodies are made on request.
Doors are of very heavy double-wall construction, braced internally.
METHOD OF VALVE ATTACHMENT.  The basic valve body has spigots on either side, for welding to a steel pipeline or to which flanges may be welded.  Alternatively, provision can be made for bolting the valve directly to a headwall structure.
A method now in common use on earth dams, is to weld the valve directly to the outfall pipe.  The pipe is made up of two welded lengths, the additional weight of pipe providing sufficient anchorage for the valve.  For valves discharging into an open channel, the spigot on the outfall side is usually of square profile.

FLOW CONTROL & SEALING
A rectangular door, with resilient seals attached to both faces, is raised or lowered within a fully enclosed body.  Guide rollers prevent twisting of the door and ensure free movement, also prevent excessive compression of the seals.  The door is forced by water pressure against one or other side of the body, compressing the seals against stainless seats.    Sealing relies on water pressure and may be less effective as pressure approaches zero.
Sealing operates in both directions, to eight metres head.  Modified versions are made for operation to  twelve metres of head.  As noted above, sealing may not be completely watertight.  Figures for permissible leakage at maximum head are given in the table below.  For special applications these figures could be reduced, although this would constitute a special valve and require detailed consideration.


Rollers are of close-grained Cast Iron, with bronze bushes, on stainless shafts.

Sectional View of Seal

Permissible Leakage Rates.

Nominal Bore (mm)

1200

1500

1800

2100

2400

3000

Max. leakage  L/min

24

30

36

42

48

60

 

SEALING COMPARISON with Batescrew HIGH HEAD VALVE.
When considering the smaller valves in the Extreme Head range, a comparison arises between these, and valves of similar configuration in our High Head range.  The latter have superior sealing characteristics, but are only rated for six metres maximum head.  For applications of less than six metres head, the High Head model would normally be preferred.  Extreme Head valves are rated at eight metres head standard and twelve metres special.
CONTROL MECHANISM   The door is raised and lowered by one or two (depending on valve size) stainless steel 'Acme' screws,  extending upwards through a bronze nut, driven by a bevel gearbox.
Two control screws, of opposite handed threads, are employed on valves of three metre bore and larger (see below).  The gearboxes share a common input shaft, to which reversible or portable drives, of any desired type, are fitted. (See 'Power Actuators'  in System Design Notes.  


Gearbox for single screw valve.
Note Hexagon boss for portable drive.
 


   Head of a 3 metre valve with two control screws.
Extended control column, on a single-screw valve.   A column of any height may be ordered, to place the drive mechanism above water, or at a convenient height, on a low-set valve.

Truss Tower.  If it is not practical to stabilize the long column against a supporting structure, a truss tower, as seen here, can be provided.