DESC:SEAT ASSEMBLY FOR SPRING LOADED GATE VALVE

Field of the invention:

The present invention generally relates to valves used for directing and controlling flow of fluids and more particularly, to a seat assembly design for a spring loaded gate valve.

Background of the invention:

A valve is a mechanical device that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids) by opening, closing, or partially obstructing the inlet and outlet ports. All valves are designed to allow/ stop the flow of a fluid through a pipeline. Spring loaded gate valves are commonly used in natural gas and oil industry. The spring loaded gate valves have two sealing faces perpendicular to the pipeline axis and its closing member is a single gate.

The spring loaded gate valve includes a valve body and a gate (obturator) which moves in a plane which is perpendicular to the direction of flow. Reciprocating motion of the gate from a first closed position to a second open position allows for fluid to flow through the valve by aligning central passage of the gate with inlet and outlet of the valve. The gate is fitted between the two spring loaded seats which provides sealing on both sides, regardless of upstream or downstream pressure conditions.

The main purpose of the spring loaded seat is to provide low pressure sealing. The spring forces the resilient seal against the valve body on the gate for the entire surface 360°. When the line pressure increases, contact load between the seat and the slab gate increases which helps valve sealing. Normally leak is observed from sealing area in low pressure air test at 5 to 80 psi.

For the leak proof sealing at metal to metal contact it is necessary to provide accurate mechanical machining and control of tolerances during manufacturing process and involves a significant increase in production cost.

Accordingly, there exists a need to design a seat which provides leak proof sealing even at low pressure service thereby overcoming the drawbacks of the prior arts.

Objects of the invention:

An object of the present invention is to obtain the optimal sealing at high hydrostatic pressure as well as at low air test pressure against traditional sealing system and to achieve double block and bleed function.

Another object of the present invention is to provide a sealing system that is free from problems deriving from presence of impurities or dirt in general in the fluid which causes gate scoring.

Yet another object of the present invention is to provide more cost effective seat assembly by reducing the machining accuracy.

Summary of the invention:

Accordingly, the present invention provides a seat assembly for a spring loaded gate valve. The seat assembly comprises a seat ring, a plurality of springs, a front side O-ring, a tail side O-ring, a poly tetra fluoro ethylene (PTFE) insert and a bonded elastomer.

The seat ring includes a plurality of holes and a serrated groove. The plurality of holes is equidistantly provided around an entire perimeter of the seat ring. The serrated groove is provided on a face of the seat ring. The plurality of springs is equally spaced and compressed into the plurality of holes of the seat ring. The front side O-ring is positioned at the front side of the seat ring as a secondary seal and is provided for restricting flow through a sealant injection. The tail side O-ring, seals a recessed annular wall on a tail side of a body portion of the spring loaded gate valve, limits the flow to the front side as a primary sealing. The PTFE insert is fitted into the serrated groove at the face of the seat ring and acts as a high pressure primary seal and as a resilient load bearing protective surface to prevent metal to metal contact during gate travel. The bonded elastomer is positioned at the face area of the seat ring and acts as a secondary seal. Specifically, the bonded elastomer used is a fluoroelastomer. The standoff of the bonded elastomer is slightly more than the height of the PTFE insert. The bonded elastomer maintains sealing even at low pressure air test from 5 to 80 psi and the bonded elastomer and the poly tetra fluoro ethylene insert facilitate achievement of a double block and bleed function.

Brief description of the drawings:

The objects and advantages of the present invention will become apparent when the disclosure is read in conjunction with the following figures, wherein
Figures 1a- 1b show a cross sectional view of an exemplary spring loaded gate valve, in accordance with the present invention;

Figure 2 is an enlarged cross sectional view showing a seat assembly for the spring loaded gate valve of figures 1a- 1b; and

Figure 3 shows a schematic diagram of a double block and bleed function of the spring loaded gate valve, in accordance with the present invention.

Detailed description of the invention:

The foregoing objects of the present invention are accomplished and the problems and shortcomings associated with the prior art, techniques and approaches are overcome by the present invention as described below in the preferred embodiments.

The present invention provides a seat assembly for a spring loaded gate valve. The seat assembly comprises a poly tetra fluoro ethylene (PTFE) insert and a bonded elastomer wherein the PTFE insert acts as a primary seal for high pressure sealing and the bonded elastomer acts as a secondary seal for low pressure sealing. As the gate penetrates downward, the seat rings are pushed back into their seat pockets causing pre-compressed springs to engage recessed seat pocket walls. Instantly, uniform mechanical force is exerted around the entire (360°) sealing surface of the seat ring as the seat ring presses on the face of the gate. The present invention of the spring loaded floating seat with the PTFE insert and the bonded elastomer takes part to auspiciously perform double block and bleed function.

This present invention is illustrated with reference to the accompanying drawings, throughout which reference numbers indicate corresponding parts in the various figures. These reference numbers are shown in bracket in the following description as well as in a table given below.

Ref. No. Component name Ref. No. Component name
2, 4 Aligned flow passages / passage ways 54 Plurality of springs
6 Body cavity 56 Front side O-ring
10 Body portion 58 Tail side O-ring
20 Slab gate 60 PTFE insert
30 Stem 62 Bonded elastomer
40 Bonnet 70 Seat assembly
50 Gate Guide 100 Spring loaded gate valve
52 Seat ring

Referring to figures 1a- 1b, a fragmentary cross-section of a spring loaded gate valve (100) (hereinafter, “valve (100)”) in accordance with the present invention is shown. The valve (100) includes a body portion (10), a slab gate (20), a stem (30), a bonnet (40), a gate guide (50) and a seat assembly (70).

The body portion (10) includes aligned flow passages/passage ways (2) and (4) and a body cavity (6). The slab gate (20) is reciprocal with the body cavity (6) and includes opening (not numbered) that is aligned within the passage ways (2) and (4) in the open position. The slab gate (20) also includes a solid portion that is adaptable to shut off the flow through the passage ways (2) and (4).

The stem (30) is attached to the slab gate (20). The stem (30) is reciprocal and sealable mounted within the bonnet (40). It is understood here that well known means to cause reciprocation of the stem (30) and the slab gate (20) is well within the purview of the present invention.

At the ends of passage ways (2) and (4) facing the body cavity (6) are machined recess walls (not numbered) that intersect the passage ways (2) and (4) and position the seat assembly (70) with reference to the gate guide (50). The gate guide (50) is used to guide the slab gate (20). Within the recess walls, the seat assembly (70) is assembled.

Referring now to figure 2, an enlarged portion of the seat assembly (70) in accordance with the present invention is shown. The seat assembly (70) comprises a seat ring (52), a plurality of springs (54), a front side O-ring (56), a tail side O-ring (58), a poly tetra fluoro ethylene (PTFE) insert (60) and a bonded elastomer (62). The seat assembly (70) holds and secures all sub components therein.

The seat ring (52) energizes the seat assembly (70) by pushing the seat assembly (70) against the slab gate (20). The seat ring (52) includes a plurality of holes (not shown) and a serrated groove (not numbered). The plurality of holes is equidistantly provided around an entire perimeter of the seat ring (52). The serrated groove is provided on a face of the seat ring (52).
The plurality of springs (54) are equally spaced and compressed into the plurality of holes of the seat ring (52). Specifically, the seat assembly (70) encompasses the equally spaced springs (54) that are compressed into equally spaced holes around the entire perimeter of the seat ring (52).

The recess annular walls of the body portion (10) are sealed at both front and tail sides by O-rings (56, 58). Specifically, the front side O-ring (56) is positioned at a front side of the seat ring (52) as a secondary seal for restricting flow through a sealant injection. The tail side O-ring (58) seals the recessed annular wall on the tail side of the body portion (10) and limits the flow to the front side as a primary sealing.

The PTFE insert (60) is fitted into the serrated groove at the face of the seat ring (52). The PTFE insert (60) acts as a high pressure primary seal and as a resilient load bearing protective surface to prevent metal to metal contact during the gate travel.

The bonded elastomer (62) is positioned at the face area of the seat ring (52) and acts as a secondary seal. The bonded elastomer (62) doubles as a low pressure seal against gate scoring by extraneous foreign particle. The bonded elastomer (62) maintains sealing even at low pressure air test from 5 to 80 psi incremented by compression of the elastic resilient member. In an embodiment, the bonded elastomer (62) used is a fluoroelastomer. However, it is understood here that any other suitable elastomer may be used in other alternative embodiments of the present invention.

Now referring to figure 3, a double block and bleed feature of the valve (100) is illustrated in accordance with the present invention. The double block and bleed feature of the valve (100) is the ability to segregate two pressure sources and bleed the pressure in the void between the two sealing elements likewise to seal the side on which pressure is applied.
In accordance with the present invention, a low pressure air seat test is conducted wherein an incremental pressure from 5 to 80 psi is applied through the flow passage (2). During pressure application, the valve (100) is in fully closed condition. The pressure applied from one side of the flow passage (2) pushes the seat assembly (70) from recess wall portion of the body portion (10). As the seat assembly (70) releases from the recess wall portion of the body portion (10), the plurality of springs (54) get released thereby causing the seat assembly (70) to come in contact with the solid slab gate (20). As such, the PTFE insert (60) makes sliding contact with the solid slab gate (20) through the entire periphery (360°).

Further, the bonded elastomer (62) also provides leak-proof seal with zero bubble droplets. The standoff of the bonded elastomer (62) is slightly more than the height of the PTFE insert (60). Thus, during sliding contact of the PTFE insert (60), the bonded elastomer member (62) gets compressed over the gate seal area and brings leak-proof seal even at low pressure air test. After the completion of testing, the seat sealing is monitored via overflow through valve cavity connection and zero bubble formation is observed through the body cavity (6) as shown in FIG 1.

Advantages of the invention:

1. The seat assembly (70) with PTFE insert (60) and the bonded elastomer (62) achieves the optimal sealing even at low pressure against traditional sealing system and achieves double block and bleed function.
2. The present invention provides sealing system which is free from the problems deriving from the presence of impurities or dirt in general in the fluid, which in the long term compromise the proper operation of the valve and the sealing of seat over the gate seal area.
3. The present invention is more cost effective to be implemented. For the leak proof sealing during metal to metal contact it is necessary to provide accurate mechanical machining and control of tolerances during the manufacturing of the parts, involves a significant increase in production cost which is overcome by the bonded elastomer (62) of the seat assembly (70).

The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, to thereby enable others skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omission and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the scope of the present invention. ,CLAIMS:We claim:

1. A seat assembly (70) for a spring loaded gate valve (100), the seat assembly (70) comprising:
a seat ring (52) having,
a plurality of holes equidistantly provided around an entire perimeter thereof, and
a serrated groove provided on a face thereof;
a plurality of springs (54) equally spaced and compressed into the plurality of holes of the seat ring (52);
a front side O-ring (56) positioned at a front side of the seat ring (52) as a secondary seal for restricting flow through a sealant injection;
a tail side O-ring (58) for sealing a recessed annular wall on a tail side of a body portion (10) of the spring loaded gate valve (100) and for limiting the flow to the front side as a primary sealing;
a poly tetra fluoro ethylene insert (60) fitted into the serrated groove at the face of the seat ring (52), the poly tetra fluoro ethylene insert (60) acting as a high pressure primary seal and as a resilient load bearing protective surface to prevent metal to metal contact during gate travel; and
a bonded elastomer (62) positioned at the face area of the seat ring (52) and acting as a secondary seal, wherein standoff of the bonded elastomer (62) is more than the height of the poly tetra fluoro ethylene insert (60).

2. The seat assembly (70) as claimed in claim 1, wherein the bonded elastomer (62) used is a fluoroelastomer.

3. The seat assembly (70) as claimed in claim 1, wherein the bonded elastomer (62) maintains sealing at low pressure air test from 5 to 80 psi, and the bonded elastomer (62) and the poly tetra fluoro ethylene insert (60) facilitate achievement of a double block and bleed function.