Guides for gate valves

A friction reducing guide is provided as an insert in the metal gate of a resilient seated gate valve. The gate is encapsulated 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.

BACKGROUND OF THE INVENTION 
This invention is in the field of gate valves for water and waste water 
service. More particularly, the invention is in the field of 
resilient-seated gate valves, e.g., those covered 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. While an inside epoxy coating is superior to 
almost all others, even the epoxy can be worn off the guide surfaces 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. The importance of the invention 
herein disclosed 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 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. A valve equipped with the present invention will, 
however, open with ease since it will have its corrosion resistant coating 
system intact even though it has been operated in service many times. 
SUMMARY OF THE INVENTION 
Plastic inserts are placed inside grooves cast in the iron gate of a 
resilient seated gate valve. A guide groove is provided in each insert. 
The guide grooves mate with guide rails cast in the valve body. This 
could, of course, be reversed with the guide grooves in the body and the 
guide rails on the gate. The gate is raised and lowered by means of a 
threaded nut and stem. The nut is retained in a cavity cast in the top of 
the gate and the shape of the cavity and nut prevent rotation of the nut. 
With the novel plastic inserts torque to raise and lower the gate is 
appreciably decreased. Resilient seated iron gate valves are, for the most 
part, provided with an epoxy coating inside the body portion and the gate 
castings of most of these resilient seated valves ae either entirely 
coated with rubber or are entirely coated with rubber except for the guide 
area. The side grooves cast in the gate have protrusions which allow the 
plastic insert 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. 
It is an object of the invention to provide a gate valve with an improved 
guide surface. It is another object of the invention to provide a gate 
valve with an improved guide surface for easier operation and longer life. 
Other objects and features of the present invention will occur to those 
skilled in the art when the following description is considered in 
conjunction with the accompanying drawings in which like numerals indicate 
like elements and in which:

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 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 FIGS. 2 and 3. FIG. 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 
FIG. 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 gates 36 and cover 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. It 
should be understood that the plastic material can be used as the inserts 
or on the guide rails whether on the gate or on the valve body. An acetyl 
copolymer of 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, Del. under 
the tradename 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. 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. 
As an alternative construction, the guide rails 48 and 50 may be covered 
with the acetyl homopolyner material and the grooves in the gate are epoxy 
coated. 
As a further alternative construction, the guide rails may be cast in the 
sides of the gate and the guide grooves may be cast in the body of the 
gate valve in place of the guide rails. In this version the plastic 
inserts are fitted into the guide grooves in the body. 
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.