GUIDES FOR GATE VALVES

Abstract: A friction reducing guide is provided as an insert in the metal gate of a resilient seated gate valve. The gate is encap­ sulated almost entirely with rubber except for the guide area. Friction is reduced and any corrosion resistant coating inside the valve body is protected, in the guide area, from excessive abrasion.

Description: This invention relates to gate valves for water and waste water service. More particularly, the invention relates to a resilient-seated gate valve. Such gate valves are specified, e.g., by ANSI - AWWA specification C-509. Resilient seated gate valves have metal gates either coated with rubber to form a resilient seat, i.e., seal, or they have a gate with a rubber seat either mechanically attached or bonded to the gate. The seat portion seals against the body of the valve after being closed by the well known means of a threaded stem and nut. The gate is guided as it descends into the valve body by grooves in the gate and mating protrusions on the body or the reverse thereof, i.e., grooves in the body and protrusions on the gate. Since such valves are almost exclusively used for water or waste water service, they are usually made of iron and the body portion is usually completely coated inside with a corrosion resistant coating. The preferred inside coating for these valve bodies is an epoxy suitable for contact with drinking water. Such a gate valve is known from the DE-OS 22 00 472. While an inside epoxy coating is superior to almost all others, even the epoxy can be worn off the guide surface after relatively few operations of the valve in service. The guide surfaces with their corrosion resistant coatings thus removed are subject to corroding. This corroding might not be a serious hazard to the valve except that it occurs on guide surfaces which must slide on either rubber coated or uncoated iron surfaces. A buildup of corrosion on these surfaces can cause excessive torque requirements to operate the valve and, in extreme cases, cause failure of the operating mechanism. These problems are solved in the DE-OS 22 00 472 by exchangeable plastic or stainless steel inserts put loosely into the grooves to prevent the epoxy coating of the grooves from a contact with the sliding parts of the gate. Furthermore, the sliding parts of the gate are provided with rolls or stainless steel bolts which slide in the inserts. This construction is intricate but nevertheless it is not free from high wear at the inserts, especially if they are made from plastic material, so that the inserts must be easily exchangable. Moreover, grains of sand can penetrate between the loosely inserted inserts and the grooves and can lift the inserts so that they can jam the gate causing an excessive torque requirement to operate the valve. The importance of the invention herein discloses is magnified when it is considered that valves in a water system may remain closed for long periods of time before operation is required. Corrosion or jam of the guide surfaces and the thousands of pounds of force against one side of the gate makes a redoubtable task of manually opening such a valve. Exchange of inserts requires a disconnection of the complete valve from the pipes and is labor-intensive. Object of the present invention is therefore a valve which can be opened with ease since it will have its corrosion resistent coating system intact even though it has been operated in service for many times. Also, during normal services an exchange of parts of the valve should not become necessary. It has now been found that the above object is achieved according to claim 1. The dependant claims relate to preferred embodiments. A valve equipped with the present invention will open with ease since it will have its corrosion resistant coating system intact even though it has been operated in service many times. In this invention the side grooves cast in the gate have depressions or projections which allow the plastic inserts having formed at their rear portion appropriate counterparts to be retained once it has been forced into place. Retention of the plastic insert is further assured once the rubber covering is bonded to the gate casting. The present invention concerns a gate valve with an improved guide surface. It also concerns a gate valve with an improved guide surface for easier operation and longer life. Other features of the present invention will occur to those skilled in the art when the following description of the invention is considered. The invention will now be described with reference to the accompanying drawings in which like elements are represented by like numerals and in which: Figure 1 is a perspective view (partially cut away) of the gate valve of the invention. Figure 2 is a top view of the gate and guide rails of the present invention taken along line 2-2 of Figure 1, and Figure 3 is a cross-sectional view of the gate valve taken along line 3-3 of Figure 2. Referring to Figure 1 there is shown a perspective view of a gate valve 10 which comprises a bonnet 12 bolted to a body 14 by means of bolts 16. A rubber or neoprene gasket 18 is held in a recess 20 in bonnet 12 and is compressed when bolts 16 are tightened. Bonnet 12 provides a housing to enclose a threaded valve stem 22 which extends through an upper opening 24 in bonnet 12 and is capped by an operating nut 26. Suitable seal-plates and o-rings, well known in the prior art are used in conjunction with the upper end of threaded valve stem 22 to prevent leakage of water around opening 24. The lower end of valve stem 22 threadedly rotates within stem nut 28 which is attached to and engages a cavity 30 cast in the top yoke 34 of gate 36 . A hollow cylindrically-shaped opening extends downwardly from yoke 34 to the bottom of gate 36 to receive valve stem 22 as the gate 36 is raised to its open position. As valve stem 22 is rotated in one direction, stem nut 28 rides upwardly over the threaded shaft of valve stem 22. When valve stem 22 is rotated in the opposite direction, stem nut 28 rides downwardly over the threaded shaft of valve stem 22. Body 14 has an entrance flange 40 and an exit flange 42 each of which have bolt holes 44 to retain flanged pipes (not shown). The central interior portion of body 14 is formed to receive gate 36 . Along the vertical centerline of body 14 is a pair of guide rails 48 and 50 which extend inwardly toward the center of the body 14. Guide rails 48 and 50 form tracks which engage guide grooves in gate 36 . Gate 36 is shown in greater detail in Figures 2 and 3. Figure 2 which is a top view of gate 36 shows stem nut 28 engaged in cavity 30 cast in the top yoke 34 of gate 36 . Cast into one side wall of gate 36 is a guide groove 54 which extends downwardly to form a track in which guide rail 48 of body 14 will lie. The other side wall of gate 36 is symmetrical and has cast-in a guide groove 56 which forms a track for guide rail 50. Within guide grooves 54 and 56 are placed inserts 60 and 62. As shown in Figure 3 depressions 64 and 66 cast into the upper rear portions of grooves 54 and 56 form seats for projections 68 and 70 at the rear of inserts 60 and 62 respectfully to anchor the inserts in the rear walls of grooves 54 and 56. The plastic inserts 60 and 62 are further held in place by guide grooves 54 and 56 being horseshoe shaped in cross section forming a dove-tailed locking system. A coating of epoxy covers the interior surfaces of bonnet 12 and body 14 protect these exposed surfaces from the effects of the fluids flowing through and within the gate valve 10. A rubber protective coating covers all of gate 36 except for the grooves 54 and 56 which receive inserts 60 and 62. Inserts 60 and 62 are held in grooves 54 and 56 by means of the rubber coating which covers the remainder of gate 36 and covers the outer edge of inserts 60 and 62. If desired inserts 60 and 62 may be bonded to the grooves 54 and 56 by epoxy or other suitable adhesives. Inserts 60 and 62 are made of a suitable plastic material of high compressive strength which does not expand when exposed to water. An acetyl copolymer or acetyl homopolymer may be used as the plastic material of inserts 60 and 62. The preferred plastic material is acetyl homopolymer such as that sold by the E.I. DuPont Company of Wilmington, Delaware under the trademark Delrin which has been found to be suitable. These acetyl homopolymers are made by the polymerization of formaldehyde and have unusual properties of high strength, rigidity, excellent dimensional stability and resilience. They maintain these properties over a wide range of useful service temperatures and humidities. Acetyl homopolymers may have a tensile strength of up to 10,000 p.s.i. and a flexural modulus of 410,000 p.s.i (1 p.s.i. = 6,6·10³Pa). Creep resistance and fatigue endurance are outstanding. The low moisture absorption gives excellent stability. The abrasion resistance of the polymer is generally superior to other thermoplastics. It has a slippery feel and has a very low coefficient of friction. Acetyl copolymers could be used for the inserts if the compresive stress was limited to that which could be withstood by the copolymer material. This of course would require a larger guide area or lower pressure allowed in the system employing the valve. Other compounds such as rubber have been tried but found to lack sufficient compressive strength. Rubber tends to wear or tear away under stress conditions and leaves a metal to metal condition which cut the rubber coating. Polyethylene and polyurethane materials have been tried but were found to be inferior to Delrin because of lower compressive strength and resulting cold flow under stress. The preferred embodiment is to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims.

Claims: A resilient seated gate valve comprising a valve body (14) coated over its entire interior surface with a corrosion resistant coating, a gate (36) coated over its surface with a rubber material, means (22, 26) for raising and lowering said gate, means for guiding said gate comprising grooves (54, 56) and guide rails (48, 50) an insert (60, 62) held inside each of said grooves and forming a groove for engaging said guide rail, characterized in that a groove (54, 56) is in each side of said gate (36) and the guide rails (48, 50) are on the inside of said valve body (14) and that said inserts (60, 62) are firmly retained in said grooves (54, 56) by projections (68, 70) and depressions (64, 66) being formed into the inserts (60, 62) and the grooves (54, 56) for engaging each other and assured once the coating of a rubber material is bonded to said gate (36) covering the outer edges of the inserts (60, 62) and all of the outside surfaces of said gate (36) except for each of said grooves (54, 56) with the received inserts (60, 62) in each side of said gate (36), said inserts (60, 62) consist of a thermoplastic or thermosetting plastic of high compressive strength so that said corrosion resistant coating on said guide rails (48, 50) is protected from abrasion and the torque required to raise and lower the gate (36) is decreased. The combination of claim 1 characterized in that said depressions (64, 66) are cast into the upper rear portion of the grooves (54, 56) to form seats for said projections (68, 70) at the rear of the inserts (60, 62). The combination of claim 1 or 2 characterized in that said grooves (54, 56) are horseshoe shaped in cross section forming a dovetailed locking system for said inserts (60, 62). The combination of any one of the preceding claims characterized in that said inserts (60, 62) are bonded to said gate (36) by an adhesive. The combination of any one of the preceding claims characterized in that said thermoplastic is an acetyl homopolymer or an acetyl copolymer. The combination of any one of the preceding claims characterized in that said thermoplastic is a poly(oxymethylene).

Inventors: BATTLE, BILLY J., JONES, LAWRENCE STEPHEN
Applicants: UNITED STATES PIPE AND FOUNDRY COMPANY
Application year: 1984
Main classification: F16K3
IPC codes: F16K3