TITLE

Penstock with resilient seal

DESCRIPTION Technical field

The invention relates to penstocks, which are large valves for controlling liquid flow, also known as sluice gates. They are predominantly used in water and sewage treatment plants.

Background of the invention

Historically, most penstocks have been manufactured from cast iron or more recently from stainless steel. Penstocks fabricated from steel generally use resilient rubber seals. Cast iron penstocks are more robust but require bronze sealing faces, which are accurately machined to close tolerances. The whole process of producing the bronze sealing faces and fixing them to the cast iron frame and door is both expensive and time consuming. The resultant product has always leaked excessively, so much so that the current British standard BS7775 allows a leakage rate of 2.5 litres per metre of sealing face per minute. This is considered inappropriate for many applications and an aim of the invention is to eliminate the majority of the leakage whilst offering cheaper materials of construction and more rapid manufacturing processes.

British patent GB 1491567 describes a method of forming the invert seal of a penstock, i.e. the seal at the base of the aperture, which the door engages as the closure of the aperture is completed. The invert seal is formed by pouring liquid urethane polymer into a channel in the base of the frame of the penstock and allowing the polymer to set. The material of the frame is not specified. The vertical seals at the side of the door are formed from strips of a semi-rigid material bonded to the frame and temporary arrangements must be provided to ensure that the vertical seals are compressed while the invert seal is poured.

Suminary of the invention

The invention provides a method of forming a resilient seal of a penstock comprising the steps of: mounting a frame of the penstock in a first orientation; pouring a liquid into a recess in the frame, which liquid subsequently sets such that the surface of the set liquid forms a resilient sealing face that is horizontal in the first orientation; after the liquid has set, mounting the frame in a second, different orientation; and pouring more of the liquid into a second recess in the frame, which liquid subsequently sets to form another resilient sealing face that is horizontal in the second orientation.

The second resilient sealing face is preferably formed to have a junction with the first resilient sealing face.

The liquid is preferably a pre-mixed two-part epoxy material.

In this specification, the use of the word "pour" to describe the introduction of the epoxy liquid into the recess is not intended to exclude supplying the liquid under pressure. The word "liquid" is not intended to exclude a paste or other formulation that is sufficiently fluid to level itself under the force of gravity before it sets.

It is preferred that the epoxy or other setting material may be allowed to cure naturally at the ambient temperature but the use of special physical or chemical methods to accelerate or improve the cure is not excluded. Temporary barriers may be provided to contain the adhesive material while in its liquid state or to allow the surface of the liquid to lie higher than the walls of the recess.

The invention also provides a penstock which comprises a frame around an aperture of the penstock; a door that can be moved into engagement with the frame to close the aperture; and a resilient seal formed in the frame by a method as previously defined.

Preferably, the penstock is closed by moving the door transversely to the aperture along an axis of movement; a sealing face of the resilient seal lies in a plane at an acute angle to the axis of movement; and the back of the door has a mating surface which lies in a plane at the same acute angle to the axis of movement such that the mating surface engages the sealing face when the penstock is closed.

Preferably, the front of the door also has a cam surface inclined at an acute angle with respect to the axis of movement, the cam surface engaging a protrusion on the frame as the penstock closes to provide a force transverse to the axis of movement that urges the mating surface of the door into engagement with the sealing face of the frame. The protrusion on the frame may be an adjusting screw, the degree of protrusion of which is adjustable to control the strength of the seal. The frame may have a plurality of the protrusions disposed around the aperture, for example four protrusions adjacent to the four corners of a generally rectangular aperture. The cam surface may be simply the angled front surface of the door or a specific cam surface may be provided to engage with each protrusion.

If the aperture is generally rectangular, then the resilient sealing face engaged by the rear surface of the door preferably surrounds at least three sides of the aperture. There may be provided a further sealing face of the resilient seal, which lies in a plane generally perpendicular to the axis of movement for mating with a leading edge of the door as it closes. Thus, when fully driven home, the door is effectively sealed on all four sides of the aperture of the penstock thereby offering a very efficient sealing area. Alternatively, and especially if the aperture is circular, a single sealing face may surround the aperture.

The drawings

Figure 1 is a front view of a penstock according to the invention in a fully closed position.

Figure 2 is a side view of the penstock in the fully closed position.

Figure 3 is a sectional side view A-A of the penstock in the fully closed position.

Figure 4 is a sectional side view B-B of the penstock in the folly closed position. Figure 5 is a front view of the penstock in a fully open position. Figure 6 is a sectional side view C-C of the penstock in the folly open position. Figure 7 is a sectional front view F-F of the frame casting showing the top and side seal.

Figure 8 is a sectional end view D-D of the frame casting showing the side and invert seals.

Figure 9 is a sectional side view E-E of the frame showing the top and invert seals.

Detailed description of a preferred embodiment

One embodiment of penstock according to the invention, as shown in the drawings, has a cast iron frame 1 surrounding a rectangular aperture 10. The door 2 of the penstock slides in guides 12 within the frame 1 and is moved by rotation of a threaded stem 5 through a similarly threaded bronze nut 3. This drives the door 2 up and down parallel to the axis of the stem 5, respectively opening or closing the aperture 10 of the penstock to the passage of liquid such as water, sewage etc.

The frame 1 includes a resilient seal around the aperture 10. A first sealing face 7 lies along three edges of the aperture 10, namely the top edge and the two side edges, as shown in Figure 7. A second, invert sealing face 8 lies along the fourth edge of the aperture 10, namely the bottom, as shown in section in Figure 9. The first and second sealing faces 7,8 meet at the bottom comers of the aperture (as shown in Figures 5 and 7) to provide a continuous seal around it. The sealing face 7 lies in a plane that is at a small angle to the axis of movement of the door 2, a typical angle being 5°. The invert sealing face 8 lies in a plane that is generally perpendicular to the axis of movement of the door 2.

Each of the sealing faces 7,8 is formed by first mounting the frame 1 using a spirit level to ensure that the desired plane of the sealing face lies perfectly horizontal. Then a two-part epoxy material, in a pre-mixed liquid form, is poured into cast recesses within the frame 1. The liquid is of a viscosity sufficient to allow it to find its own level before it cures, whereby when the liquid sets the surface provides a flat,

square, resilient sealing face 7,8. The epoxy material naturally adheres to the substrate of the frame 1 so that the seal is secured in place. If required, the base or sides of the recess may be profiled so as to provide an increased surface area for adhesion or to physically engage the seal to hold it in place. On full cure, the epoxy material may have a Shore hardness of more than 50, preferably about 60.

When one sealing face 7,8 has been formed and has cured sufficiently, the frame 1 is remounted in a desired orientation and the process is repeated to form the other sealing face 8,7. The two faces may be formed in either order. The two faces meet at each of the lower corners of the aperture 10 as shown in Fig. 6 and, being of the same material, they naturally bond strongly to one another. It is evident that more than two sealing faces could be provided by proceeding in a similar manner.

The door 2 has angled faces on the front and back, as shown in Figures 4 and 6, so as to be generally wedge-shaped overall. The back face 14 of the door 2 is generally planar and is parallel to the first sealing face 7 so that it can form a tight seal therewith. The angle of the sealing face 7 relative to the axis of movement means that the force driving the door 2 closed as the stem 5 rotates has a component that is perpendicular to the sealing face 7, thereby strengthening the seal. The bottom edge of the door 2 is square to the sides and coincides with the invert sealing face 8 in the bottom of the frame 1. Thus, as the penstock closes, the force acting along the stem 5 drives the bottom, flat edge of the door 2 into the resilient invert face 8.

The angled front face 16 of the door 2 carries four cam surfaces 18 in the form of ramps or wedges; and the correspondingly angled front part of the frame carries four adjusting screws 4, which protrude into the cavity in which the door 2 slides. As the penstock is closed by lowering the door 2 from the position shown in Figure 6 to the position shown in Figure 4, the tips of the adjusting screws 4 act on the cam surfaces

18 to divert some of the longitudinal movement of the door 2 into transverse movement and urge the back surface of the door 2 into still closer engagement with the sealing face 7 on the frame 1. Because of the overall angle of the front face 16 of

the door 2, the lower pair of cams 18 clear the upper pair of adjusting screws 4 as the door 2 is lowered.

The threaded adjusting screws 4 may be individually adjusted and locked in place by locknuts 6 to change the degree of protrusion into the cavity, whereby the strength of seal can be adjusted and balanced at all four corners of the door 2.

The resultant assembly is capable of withstanding the pressure created by the flow of liquid and forms an efficient seal to prevent excessive leakage through the orifice.