GB2168504A - Pressure-reducing-valve - Google Patents

Abstract

In a pilot-type pressure reducing valve wherein both the main and pilot valves (5, 11 Fig. 1) are associated with a plunger structure comprising a movable inner and a stationary outer member, at least one of the inner members includes a seal formed by at least two axially-spaced split annular sealing members 8 or 19 of fluorine resin. <IMAGE>

Description

SPECIFICATION Pressure reducing valve This invention relates to a pilot-type pressure reducing valve for example for use in a piping system for steam, compressed air or the like, for maintaining secondary fluid pressure at a predetermined set value.

As described, for example, in the Japanese utility model publication No. 45-27184, a pilot-type pressure reducing valve includes a pilot valve, in addition to a main valve, disposed in a fluid path communicating the primary side of the main valve with a cavity above a piston interlocked with the main valve for controlling it. The pilot valve is controlled by a diaphragm which deflects in response to fluid presure in the secondary side of the main valve, to control the amount of fluid flowing into the above cavity, thereby driving the piston and the main valve, interlocked therewith, in accordance with a pressure difference between the upper surface of the piston and its lower surface which is subject to the secondary atmosphere.

The piston and pilot valve of a pressure reducing valve of this type effect delicate motion in accordance with the primary and secondary side pressures, as described above, and have substantial influence upon the operational characteristics of the valve itself. More specifically, as to the piston, the fluid pressure acting on the upper surface thereof is controlled by leaking the primary fluid having flowed into the cavity above the piston through the pilot valve, through a gap between the piston and cylinder. If this gap is small, the leakage of fluid is also small and this may result in the main valve being left as open and/or the piston being burnt to the cylinder. If the gap is widened enough to prevent such trouble of burning seizure, the leakage will become large to reduce the force for driving the main valve.As for the pilot valve, if the primary fluid flows through a gap between a pilot stem and a stem guide into a cavity under a diaphragm (hereinunder referred to as "diaphragm chamber"), the pressure in the diaphragm chamber, which has initially to be the secondary pressure, varies and, consequently, the diaphragm whose operation is subject to this pressure may operate erroneously. If the gap is made narrower to prevent the leakage, however, the increased slide resistance will disturb smooth motion thereof.

Thus, it is desired to provide such slide portion with a structure having high sealing power and low slide resistance.

In order to attain the above object, in the above-cited Japanese publication, a fixed gap is formed between the piston and cylinder and a metal ring is disposed in an annular groove formed in the side wall of the piston to allow the fluid above the piston to leak through the gap between the metal ring and the cylinder.

However, such structure may result in unstable motion of the slide portion, which causes erroneous operation as a whole. More specifically, the metal ring, which is made typically of phosphorus bronze, gives non-uniform leakage between the metal ring and the inner cylinder surface due to irregularity of its outer diameter, and sometimes causes seizure of the slide portion due to thermal expansion, which may result in erroneous operation.

According to the invention, there is provided a pressure reducing valve comprising a main valve and a pilot valve, each said valve being associated with a plunger structure comprising a movable inner member having a cylindrical outer surface and a stationary outer member having a cylindrical inner surface facing said outer surface of said inner member for controlling said valve, wherein at least one of said inner members has at least two annular grooves spaced apart axially from each other in the outer surface thereof, each said groove containing at least one annular sealing member, each said sealing member being made of fluorine resin and split at least at a part thereof.

Preferably, the first and second members may be a piston and cylinder, respectively, for controlling the main valve, or a pilot stem and stem guide, respectively, for controlling the pilot valve.

An embodiment according to the invention will now be described by way of example only with reference to the accompanying drawnings, in which: Figure 1 is a sectional side view of an embodiment of a pressure reducing valve according to the invention; Figure 2 is an enlarged partially sectional side view of a piston-cylinder structure of the pressure reducing valve of Fig. 1, and Figure 3 is a an enlarged sectional side view of a pilot valve structure of the pressure reducing valve of Fig. 1.

Throughout the drawings, the same reference numerals are given to corresponding structural components.

Referring to Fig. 1, an embodiment of pressure reducing valve according to this invention includes a trap body 29 having a lower cover 31 for containing a float 34, a main body 1 for containing a piston 6, a cyinder 9, a main valve 5 and a separator structure including swirl vanes 27 and a drain member 28, a pilot body 32 for containing a pilot valve 11, and a spring casing 33 for containing a pressure setting spring 14. These components are coupled in this order, as shown in the drawing, by their flanges with suitable gakets disposed therebetween. A diaphragm 15 is disposed between the pilot body 32 and spring casing 33.

The main body 1 has inlet port 2 and anoutlet port 3 formed coaxially with each other and connected mutually through a valve port 4. The main valve 5, which is urged upwards by a spring against a valve seat formed around the valve port 4, has a central pin extending upwards and butting within valve port 4 against the bottom end of a piston pin extending downwards from piston 6.

The pilot valve 11 is disposed between a communication hole 12 for a cavity under main valve 5 and another communication hole 13 for a cavity above piston 6, and urged upwards by a spring against diaphragm 15.

On the other hand, the diaphragm 15 is urged through a spring pad 23 by means of pressure setting spring 14 whose compressive force can be adjusted by an adjusting screw 22. A chamber under diaphragm 15 (that is the diaphragm chamber) is connected through a communication hole 26 to outlet port 3, while a chamber above diaphragm 15 is connected through a communication hole 25 to the external atmosphere.

The drain member 28 is disposed with a screen 32 within the space under the valve port 4. The drain member 28 includes two coaxial cylindrical members, the inner one of which has its lower end expanded, and a plurality of swirl vanes 27 are arranged between the inner and outer members.

Within the trap body 29, a hemispherical float cover 35 having a plurality of through holes 36 is supported over the bottom plate or cover 31 by suitable means, not shown, and a hollow spherical float 34 is contained freely within the space between cover 35 and bottom plate 31.The bottom plate 31 has a drain port 37 provided with a drain valve seat 38 which is normally closed by the float 34 as a valve body.

In operation, the main valve 5 is normally closed by the spring force acting upwards thereon and the pilot valve 11 is normally opened by a preset downward spring force of pressure setting spring 14 adjusted previously by adjusting screw 22. When steam containing water enters the inlet port 2, its pressure is communicated through communication hole 12 to the cavity under pilot valve 11 and then to the cavity above piston 6 through the open pilot valve 11 and communication hole 13, to push piston 6 downwards thereby opening the main valve 5. Thus, the steam enters the trap 29, passes through the opened main valve 5 and then exits from the outlet port 3. During this passage of the steam, the swirl vanes 27 swirl the steam to separate the water by centrifugal force to cause it to pool in the bottom of trap 29 as drainage.When the drainage is accumulated enough to overcome the weight of float 34, the float 34 leaves the valve seat 38 to permit discharge of the drainage from drain port 37.

The steam pressure is also communicated through communication hole 26 to the diaphragm chamber. If the steam pressure rises above a preset value it pushes the diaphragm 15 against the spring 14. This results in closure of pilot valve 11, which is urged upwards by a spring as shown, and consequent balance in pressure between the upper side and underside of piston 6 due to leakage through an orifice 10 (Fig. 2) of piston 6. Accordingly, main valve 5 is closed by the spring force backed up by the steam pressure in the primary side, to stop the steam flow.

The same operation is repeated with variation in the primary steam pressure to regulate its seconday pressure at the preset value.

Fig. 2 shows the piston structure of the above described valve. The structure includes a piston cylinder 9 and the piston 6 which is inserted into the cylinder 9 leaving a small gap therebetween. The piston 6 has an orifice 10 for connecting its upper side and underside for the abovementioned purpose. Two annular grooves 61 are formed spaced apart from each other in the cylindrical outer wall and an annular ring-shaped sealing member 8 is fitted in each groove 61. The sealing member 8 is made of fluorine resin and split at least at a part 62. A leaf spring 7 is disposed between each sealing member 8 and the bottom of its groove 61 to urge the sealing member 8 against the inner surface of the cylinder 9 in order to assure an intimate contact therebetween.

Referring to Fig. 3, the pilot valve structure 11 comprises a stem guide 16 and a pilot stem 17 inserted into a guide hole 161 of the former. A valve seat 162 is formed around the lower end of the guide hole 161 fo contact with a valve body 21 of pilot stem 17.

Intersecting the guide hole 161, a horizontal through-hole 18 is formed in the stem guide 16 and connected to communication hole 13 (Fig. 1) for the abovementioned purpose.

The pilot stem 17 is composed of a spindle 171 with a diameter substantially less than the inner diameter of guide hole 161 of stem guide 16. The spindle 171 has a flange-like enlarged portion 172 formed integrally therewith just above the through-hole 18, a valve body 21 fixed to the lower end and a top member 173 press-fit on the top and a sleeve 20 slidably fitted on the spindle 71 between both elements 172 and 173. The elements 20, 172 and 173 have a diameter slightly less than the inner diameter of the guide hole 161.

In grooves defined by and between the elements 20 and 172 and the elements 20 and 173, a pair of annular sealing members 19 are disposed respectively. Each member 19 is made of fluorine resin and split at least at a part 191. The axial dimension of the elements 19 and 20 are designed so that the sum of them is less than the spacing between the elements 172 and 173 and substantial axial movement of the elements 19 and 20 is allowed. Such designs enables absorption of possible thermal expansion of the sealing members 19 in both axial and radial directions to prevent the aforementioned problem of seizure. On the top member 173, a domed cap 24 is provided for contact with the diaphragm 15 (Fig. 1).

As described above, the sealing members 8 and 19, made of fluorine resin and split at least at a part (62, 191) thereof, exhibit substantially reduced slide resistance and effectively absorb their thermal expansion, if any, and their axial separation on each piston 6 or pilot stem 17 can avoid any inclination thereof which may result in non-uniform contact, thereby maintaining constant smooth operation of the valve.

The slidable portions of both the main valve and the pilot valve are thus modified to exhibit high sealing power and low sliding resistance and to avoid seizure due to thermal expansion.

Claims (6)

1. A pressure reducing valve comprising a main valve and a pilot valve, each said valve being associated with a plunger structure comprising a movable inner member having a cylindrical outer surface and a stationary outer member having a cylindrical inner surface facing said outer surface of said inner member, for controlling said valve, wherein at least one of said inner members has at least two annular grooves spaced apart axially from each other in the outer surface thereof, each said groove containing at least one annular sealing member, each said sealing member being made of fluorine resin and split at least at a part thereof.

2. A pressure reducing valve as claimed in claim 1, wherein an elastic member is disposed between the bottom of a said groove and the corresponding said sealing member, for urging said sealing member against the inner surface of said outer member.

3. A pressure reducing valve as claimed in claim 2, wherein said elastic member is an annular leaf spring.

4. A pressure reducing valve as claimed in any of the preceding claims, wherein at least one of said inner members is a piston and its corresponding outer member is a cylinder, said piston including an orifice communicating with both sides thereof.

5. A pressure reducing valve as claimed in any of the preceding claims, wherein at least one of said inner members is a pilot stem, and its corresponding outer member is a stem guide, said pilot stem having a diameter reduced over an intermediate portion thereof leaving it unchanged at both side portions of said intrmediate portion, a cylindrical sleeve being slidably fitted on said intermediat portion, and said sealing members being disposed around said intermediate portion between said sleeve and said side portions keeping some axial and radial clearances.

6. A pressure reducing valve substantially as herein described, with reference to the accompanying drawings.