AU722486B2 - Pressure relief device - Google Patents

Description

AUSTRALIA

PATENTS ACT 1990 TRUE COPY .i b ac a a a COMPLETE SPECIFICATION We, YORKSHIRE FITTINGS PTY LTD certify that the following 9 pages are a true and correct copy of the description and claims of the original complete specification in respect of an invention entitled: "PRESSURE RELIEF DEVICE" Name of Applicant: YORKSHIRE FITTINGS PTY LTD a.

*e 0 0*a* by 1- s Fellow Institute of Patent Attorneys of Australia of SHELSTON WATERS Signature:

,A

-2- The present invention relates generally to pressure relief valves.

The invention has been developed primarily for use as an auxiliary pressure relief valve for use in water heaters and will be described hereinafter with reference to this application. It will be appreciated, however, that the invention is not limited to this particular field of use.

Pressure relief valves presently available are designed to offer safety protection for unvented water heaters. Such valves commonly comprise a valve member resiliently biased against a seat by a valve spring. When the pressure in the hot water tank exceeds S°a predetermined limit, the relief valve is caused to "blow off' whereby the valve member temporarily lifts off its seat, thereby releasing the excess pressure and relieving stress on the hot water cylinder.

A problem arises, however, if this pressure relief occurs when the water in the tank is overheated. In such circumstances, the boiling point of the water drops dramatically with the release of pressure, causing the superheated water to flash 15 instantaneously into steam, with explosive force. This is a common cause of ruptures and explosions in water heaters.

In order to address this problem, hot water pressure relief valves are often additionally provided with an independent thermal relief mechanism. This typically comprises a wax-filled temperature probe, which expands under dangerously high temperature conditions, to mechanically lift the valve member from its seat until cooler liquid surrounds the probe, allowing the wax to contract and re-seat the valve. The set temperature is normally well below 100 0 C, to ensure that the water in the tank never becomes superheated and potentially explosive, even in the event of thermostat failure.

-3- When the relief valve operates to vent the tank, either under conditions of excess temperature or pressure, surplus water flows through a discharge line to drain.

Occasionally, however, the discharge line itself can become damaged or blocked, in which case the pressure relief valve may not function to relieve pressure in the tank. In order to overcome this problem, an auxiliary pressure relief valve is commonly fitted to the discharge port of the primary relief valve.

S. These auxiliary valves normally incorporate some form of rubber plug which S. seals an auxiliary discharge port. The plug is configured such that if a predetermined 99 9 9• 9 threshold pressure is exceeded in the discharge line of the primary valve, the plug will blow, venting the primary discharge line to atmosphere via the auxiliary discharge port.

Thus, the auxiliary pressure relief valve acts as a mechanical "fuse" in the system.

There are, however, several problems with the existing design of such auxiliary °9 pressure relief valves. Firstly, the plug is not re-seatable and consequently, the auxiliary valve must be discarded and replaced whenever it is tripped. This is a time consuming, 15 inconvenient and costly process. Secondly, the auxiliary discharge port itself can become blocked by the blown-off plug, which in some cases can result in failure of the auxiliary valve altogether, with potentially dangerous consequences. Thirdly, because of the disposable nature of known auxiliary pressure relief valves, and by virtue of their inability to be re-seated, they need to be manufactured as a separate replaceable component and hence cannot be fully integrated with the primary valve. This in turn adds to the overall cost and complexity of the valve assembly as a whole. Furthermore, it is difficult to achieve accurate and consistent relief pressure thresholds with known valve designs.

-4- It is an object of the present invention to overcome or ameliorate at least some of the disadvantages of the prior art.

Accordingly, the invention consists in an auxiliary pressure relief valve for use with a primary pressure relief valve, said auxiliary pressure relief valve including: a housing defining a passage adapted for fluid communication with a pressure chamber associated with said primary pressure relief valve; a body formed substantially from a resiliently deformable material and disposed in said housing for deformation between a closed configuration wherein said body seals S: said passage and an open configuration wherein said body resiliently deforms to permit fluid flow around the body and through the passage in response to an increase in fluid So o* opressure within said pressure chamber beyond a predetermined threshold level; and restraining means to locate said body within said passage such that the body resiliently returns to the closed configuration when the pressure in said chamber drops below said predetermined threshold level.

15 Preferably, the body is a rubber sphere urged into sealing engagement with a mouth of said passage by said restraining means.

Preferably also, the restraining means includes a plurality of spaced apart prongs against which the resilient body deforms such that in the open configuration, escaping fluid flows around the body and the prongs, through the passage, thereby venting the pressure chamber to atmosphere. The prongs preferably form part of a spider assembly disposed within the housing.

In the preferred embodiment, the pressure relief valve functions as an auxiliary pressure relief valve to a primary relief valve of a hot water storage tank. In this case, a discharge port of the primary relief valve preferably forms the pressure chamber of the auxiliary pressure relief valve, such that the auxiliary pressure relief valve is operable in the event of the primary discharge port becoming blocked.

A preferred embodiment of the invention will now be described, by way of example only, with reference to accompanying drawings in which: Figure 1 is a sectional side elevation of a conventional primary pressure and temperature relief valve for a hot water storage tank, incorporating an auxiliary pressure relief valve in accordance with the invention; Figure 2 is an enlarged cross-sectional view showing the auxiliary pressure relief valve of Figure 1 in more detail; and Figure 3 shows an alternative embodiment of the auxiliary pressure relief valve of Figure 2.

Referring to the drawings, figure 1 shows a combination pressure temperature relief valve assembly, for use with a domestic hot water storage tank (not shown). The .15 assembly comprises a conventional primary pressure and temperature relief valve 1 and an auxiliary pressure relief valve 21 according to the present invention.

The primary relief valve 1 consists of a valve body 3 incorporating an annular valve seat 6. In the applicant's product the seat 6 is made of marine grade stainless steel, which is resistant to corrosion caused by chlorine and abrasion caused by impurities often found in water such as dust and scale, although other suitable materials may be used. The valve seat 6 is sealed by a silicon disk 7 which is also resistant to continuous heat and abrasion. The disk 7 is permanently swaged into a subassembly incorporating a flexible joint to ensure positive reseating. The subassembly 10 supports a compression spring 15, designed for the required set pressure. The spring 15 is enclosed between a flexible diaphragm 12 and a retainer subassembly 16, and is thereby free from direct contact with moisture from the tank.

A thermal probe 13 is supported by a probe retaining bracket 14 and extends below the seat 6 into the water tank. The probe 13 typically consists of a conductive copper tube filled with wax which expands or contracts in response to temperature changes in the water within the tank. Expansion of the wax pushes the disk 7 upwardly from its seat 6 by means of a push rod 15. The probe 13 itself is usually enclosed in an outer tube or sleeve 16, preferably formed from polyolefin, to avoid mineral build up and 10 galvanic corrosion on the exposed copper element, which may otherwise break off and foul the valve seat.

e S"In use, either excessive temperature or pressure conditions cause the disk 7 to lift from the valve seat 6, thereby venting the water storage tank to atmosphere via annular S.discharge port 17 and drain line 18. Manual pressure relief can be achieved by an external lever assembly 19.

S .As best shown in figure 2, the present invention provides an auxiliary pressure relief valve 21 including a housing 22 defining a passage 23 in selective fluid communication with the discharge port 17 of the primary relief valve 1. In this case, the housing is integrally cast with the body of the main valve but may alternatively be threadedly or otherwise releasably secured to it. The auxiliary valve 21 includes a body formed from resiliently deformable material, preferably in the form of a rubber ball or sphere 24, disposed within the housing 22 and normally retained in sealing engagement with the mouth of passage 23 by restraining means 26. The restraining means comprises a spider assembly against which the rubber sphere 24 can deform to allow fluid to flow through the passage 23, and out through an auxiliary discharge vent 27 to atmosphere, as described in more detail below. As best shown in figure 2, the spider assembly comprises a plastic plug 28, which is screwed into releasable threaded engagement with the housing 22. The plug defines three angularly spaced prongs 28 which engage the rubber sphere 24. Pressure setting of the valve assembly 21 is preferably achieved by selection of the material of the rubber sphere 24 and of the pressure applied thereto by the spider assembly 28.

Figure 3 shows an alternative embodiment of the spider mechanism, wherein 10 each prong 28 of the retaining plug 26 includes an outwardly depending lug 29 ***.configured releasably to engage a corresponding recess 30 formed in the housing 22. The S°lugs 29 are resiliently biased outwardly into locking engagement with the respective recesses to secure the spider in position, and may be retracted using a suitable tool to o permit replacement of the spider if necessary.

In operation, the relief valve assembly is fitted near the top of the main hot water storage tank. If either the pressure or the temperature in the storage tank exceeds a predetermined threshold level, the disk 7 of the primary valve lifts off its seat, to vent the tank via discharge port 17 and drain line 18, in the conventional manner. However, if the drain line becomes blocked, excess pressure from the tank will accumulate in the discharge port 17. If this pressure exceeds a predetermined threshold value, the rubber sphere 24 of the auxiliary pressure relief valve is resiliently compressed outwardly against the retaining prongs 28 of the spider into an open configuration. The resultant localised deformation of the rubber sphere against the prongs permits the pressurised -8fluid to flow around the sphere, past the prongs, and through the auxiliary discharge vent 27 to atmosphere. When the pressure in the storage tank drops below the threshold level, the sphere 24 relaxes resiliently into the closed configuration, and is automatically reseated into sealing engagement with the mouth of passage 23.

It will be appreciated that the pressure relief valve of the present invention can be used effectively as an auxiliary valve to prevent explosion or rupture of pressurised storage containers in the event of failure or blockage of the primary valve. Furthermore, it is relatively inexpensive to produce with a minimal number of components, and because it is automatically re-seating, can be integrally formed with the body of the main 10 valve. It may, however, also be used directly as a primary relief valve.

Although the invention has been described with reference to specific examples, it ooo• °will be appreciated by those skilled inthe art that the invention may be embodied in many other forms.

ao a

Claims (9)

1. An auxiliary pressure relief valve for use with a primary pressure relief valve, said auxiliary pressure relief valve including: a housing defining a passage adapted for fluid communication with a pressure chamber associated with said primary pressure relief valve; a body formed substantially from a resiliently deformable material and disposed in said housing for deformation between a closed configuration wherein said body seals said passage and an open configuration wherein said body resiliently deforms to permit fluid flow around the body and through the passage in response to an increase in fluid 10 pressure within said pressure chamber beyond a predetermined threshold level; and 0. restraining means to locate said body within said passage such that the body resiliently returns to the closed configuration when the pressure in said chamber drops .00. below said predetermined threshold level.

2. An auxiliary pressure relief valve according to claim 1, wherein the body is urged -15 into sealing engagement with a mouth of said passage by said restraining means. ooo.

3. An auxiliary pressure relief valve according to claim 1 or claim 2, wherein the restraining means include a plurality of spaced apart prongs against which the resilient body deforms such that in the open configuration, escaping fluid flows around the body and the prongs, through the passage, thereby venting the pressure chamber to atmosphere.

4. An auxiliary pressure relief valve according to claim 3, wherein the prongs form part of a spider assembly disposed at least partially within the housing.

An auxiliary pressure relief valve according to any one of the preceding claims wherein said restraining means is adjustable to alter the predetermined threshold level.

6. An auxiliary pressure relief valve according to claim 5 wherein said restraining means is adapted for threaded engagement with said housing, the predetermined threshold level being adjustable by selectively rotating the restraining means with respect to the housing.

7. An auxiliary pressure relief valve according to any one of the preceding claims, wherein the body is a rubber sphere.

8. An auxiliary pressure relief valve according to any one of the preceding claims, 10 adapted for use with a primary pressure relief valve of a hot water storage tank. o:

9. An auxiliary pressure relief valve according to claim 8, wherein a discharge port -"of the primary pressure relief valve forms the pressure chamber of the auxiliary pressure relief valve which is operable in the event of the primary discharge port being blocked. An auxiliary pressure relief valve as hereinbefore described with reference to 15 Figures 1 and 2 or Figure 3. DATED this 16th Day of September, 1996 "YORKSHIRE FITTINGS PTY LTD .ooo.i Attorney: CAROLINE M. BOMMER Fellow Institute of Patent Attorneys of Australia of SHELSTON WATERS