AU709265B2 - A temperature probe - Google Patents

Description

The present invention relates to a temperature probe.

The invention has been developed primarily for use with safety release valves for domestic hot water heating systems and will be described hereinafter with reference to that application. However, it will be appreciated that the invention is not limited to that s particular field of use.

Hitherto, temperature probes for safety release valves have included a metallic tubular body for housing an expansion element, generally of wax or wax impregnated with metal powders. An increase in temperature causes expansion of the wax which subsequently mechanically actuates a release valve or the like.

In an attempt to provide actuation of the release valve at a predetermined temperature use is made of waxes which undergo substantially all their thermal expansion in a critical temperature range. However, tolerances in the dimensions of the tube and was element result in significant variation of actuation temperatures.

It is an object of the present invention, at least in the preferred embodiment, to S 15s overcome or substantially ameliorate this disadvantage of the prior art.

According to a first aspect of the invention there is provided a temperature probe, the probe including: *an axially extending tubular body; °an expansion element disposed within the body adapted to expand in response to an increase in the temperature of the probe; a stem slidably mounted in the body and adapted to progress axially in response to expansion of the element; a first seal slidably and sealingly engaged with the body adjacent the stem; to. a second seal fixedly disposed within the tubular body; and a liquid for occupying voids between the element and the body to ensure that substantially all of the thermal expansion of the element occurs in the axial direction, t wherein the expansion element extends between a first end adjacent the first seal and a second end adjacent the second seal.

Preferably the stem is axially progressable into opening engagement with an adjacent valve.

More preferably, the valve is a safety release valve for a hot water system.

More preferably, the expansion element includes a precise point expansion wax.

C 4) More preferably, the wax has a break point of about 101 C although other embodiments 4- include a break point of about 90 0

C.

[R:\LIBLL]07884.doc:MFF:DMB Preferably also, the liquid is a mineral oil based heat transfer media. More preferably, the media and the wax are substantially immiscible.

According to a second aspect of the invention there is provided a method for manufacturing a temperature probe including the steps of: inserting a first seal into an axially extending tubular body for sealingly engaging against the inner surface of the body; inserting a liquid and an expansion element having a first end and a second end into the body whereby the liquid is disposed radially between the element and the body and the first end is adjacent to the first seal; and inserting a second seal into the body adjacent to the second end, the second seal being slidably mounted for progression along the body in response to thermal expansion of the element.

Preferably, the method also incudes the step of inserting a stem into the body, wherein the stem at one end abuts the second seal and at the other end protrudes from the body.

i [R:\LIBLL]07884.doc:MFF:DMB -4- Preferably also, the second seal is abutted against the second end prior to sealing against the body. More preferably, the second seal abuts both the liquid and the second end prior to sealing against the body.

A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a cross sectional view of a temperature probe according to the invention; Figure 2 is a cross sectional view of a domestic hot water safety release valve •including the temperature probe of Figure 1;

S

10 Figures 3(a) through to 3(1) inclusive illustrate a sequence of forming a probe according to the invention; and Figure 4 is an enlarged partial cross-section of area A of Figure 3(a).

Referring to the drawings, and in particular to Figure 1, a temperature probe 1 includes an axially extending tubular copper body 2 extending between two open ends 3 and 4. A cylindrical wax expansion element 5 is disposed within body 2 for expanding in response to an increase in temperature of the probe. A liquid 6 fills the voids between element 5 and body 2 to ensure that substantially all the thermal expansion of the element occurs in the axial direction.

Element 5 extends between a first end 9 and a second end 10 which respectively abut opposed rubber seals 11 and 12. Although seal 12 is maintained in a fixed configuration by an adjacent brass or stainless steel plug 13, seal 11 is slidably mounted within body 2 and moves along the body following expansion of element A stem 14 extends between a first end 15 which abuts seal 11 and a second end 16 which protrudes from body 2 for selective movement into opening engagement with an adjacent safety valve diaphragm 17, as best illustrated in Figure 2.

More particularly, a safety release valve 51 includes a housing 52 which defines two chambers 53 and 54 which are separated by diaphragm 17. Chamber 53 is in fluidic communication with an adjacent hot water heating tank (not shown) into which probe 1 extends. Should the temperature of the water in the tank and surrounding probe 1 rise, wax element 5 will expand and in turn progress end 16 of stem 14 into engagement with diaphragm 17. Accordingly, the water contained in chamber 53 can now flow into chamber 54 and through an outlet In the embodiment shown probe 1 is sheathed with a plastics heat shrink sleeve 56 to provide superior corrosion resistance. Other appropriate sleeves are known to those skilled in the art.

Preferably, element 5 is a precise point expansion wax produced by Huls AG and designated DW101. It will be appreciated, however, that other waxes are used in other embodiments particularly where the probe operates at different temperatures.

Preferably also, liquid 6 is a mineral oil based heat transfer media sold by Mobil under the product name Mobiltherm 603. Again, alternative oils and liquids will be known to those skilled in the art.

The abovementioned wax and oil are preferred because they remain substantially immiscible in the intended operating range. Accordingly, probe 1 is a multi-use device.

However, in alternative embodiments probe 1 is configured for single use and element upon melting, mixes with liquid 6.

-6- In the described embodiment, body 2 is approximately 98mm long and has an internal diameter of about 4.89mm. The element 5, however, is about 36mm long and has an external diameter of about 4.8mm. Due to manufacturing tolerances the volume of liquid 6 contained between seals 11 and 12 varies for each particular probe.

Alternative dimensions for body 2 and element 5 are possible.

It is preferred that body 2 is crimped at or adjacent to end 4 to captively retain plug 13 within the body. In some embodiments plug 13 includes a plurality of axially spaced apart circumferentially extending grooves into which body 2 progresses during the crimping operation to ensure an interference fit between the two components.

Referring now to Figures 3(a) to where corresponding features are denoted by corresponding reference numerals, a particularly preferred method of manufacturing temperature probe 1 will be described.

Initially, a tubular billet is cut from a hard drawn copper tube (not shown) which is formed into body 2. Copper is a preferred material due to its corrosion resistance and o.

good thermal conductivity.

End 3 of body 2 includes a cold formed flange 17 and an adjacent radially expanded portion 18. Additionally, end 4 is formed to provide an inwardly extending annular lip 19 which is shown in more detail in Figure 4. The body 2, thus formed and as illustrated in Figure is loaded onto the first station of a carriage (not shown) for subsequent operations.

Referring in particular to Figure 4, lip 19 is substantially annular and includes a first and a second surface 81 and 82 which are outwardly and inwardly directed respectively.

-7- The carriage presents body 2 at the second station, as best shown in Figure 3(b), where the plug 13 is inserted into end 3 and falls to end 4 to rest against surface 82 of lip 19. At a third station, as best shown in Figure a first press 20 inserts seal 12 into end 3 of body 2 and subsequently withdraws. Preferably, seal 12 is disposed at a predetermined position along body 2. Preferably, the distance between flange 17 and seal 12 is less than the length of element At a fourth station, shown in Figure the oil 6 or other liquid heat transfer media is metered into end 3 of body 2 and collects adjacent to seal 12. Body 2 is then progressed to a fifth station, best shown in Figure where a second press 21 moves into end 4 of body 2 and progresses plug 13 upwardly into engagement with seal 12 to positively locate the seal at a predetermined location within the body 2. Thereafter, wax expansion element 5 is inserted into end 3 of body 2. Preferably, element 5 is a close fit *oo within the body 2.

While at the sixth station a third press 22 slowly downwardly progresses element 15 5 into body 2 until the face 23 of press 22 engages end 3. As shown in Figure press 21 may have to be partly withdrawn to accommodate such engagement. It is preferred that seal 12 and plug 13 are downwardly progressed to some extent to ensure that substantially any voids between element 5 and body 2 are filled with oil 6.

It will be appreciated that the volume of oil 6 is sufficient to cause some overflow from end 3 once element 5 is inserted to ensure a substantial removal of gases from between element 5 and body 2.

The partly assembled probe is then moved to a seventh station shown in Figure where seal 11 is inserted into end 3. Preferably, the insertion of seal 11 effects -8some downward progression of element 5 and seal 12. Preferably also, seal 11 simultaneously abuts element 5 and liquid 6 to ensure an absence of gases between the seals. However, in some embodiments, seal 12 abuts oil only.

As shown in Figure press 21 has been withdrawn and accordingly plug 13 may drop to end 4.

At a eight station shown in Figure element 5 and the surrounding seals 11 and 12 are located at a predetermined distance L from end 3 by a fourth and a fifth press 23 and 24. Thereafter, body 2 is crimped by press 25 adjacent to end 4 to secure plug 13 in a fixed configuration and thereby ensure that any expansion of element 5 will result in movement of seal 11 only.

probe is then moved to a ninth station, illustrated in Figure where stem 14 is inserted into end 3 of body 2, to abut against top face of seal 11.

At the tenth station, as illustrated in Figure a press 26 applies a predetermined axial force to end 16 of stem 14 to load test the crimped joint between plug 13 and body 2. Ifthe joint fails the load test, probe 1 is rejected.

The assembled probe is progressed to an eleventh station, as shown in Figure where an inspection is made of the distance H that end of 16 stem 14 protrudes beyond end 3. In practice, the distance measured is that between the underside of flange 17 and end 16 of stem 14. Should this distance fall outside predetermined limits, probe 1 is rejected.

The resultant temperature probe 1 is advanced to a twelfth station, as best shown in Figure and ejected from the carriage by a press 27.

-9- The use of oil 6 or other suitable fluid provides a temperature probe which can very accurately actuate a safety release valve, notwithstanding the usual manufacturing tolerances associated with the sizing of the copper tube and the element itself.

Additionally, the above described preferred method of manufacturing the probe lends itself to mechanisation and self-checking to further enhance accuracy.

The oil has good thermal conductivity and occupies only a small percentage of the volume of body 2. Accordingly, it will be element 5 which will account for substantially all the expansion occurring within body 2.

"Although the invention has been described with reference to a particular example, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.

a a °ooE The claims defining the invention are as follows: 1. A temperature probe, the probe including: an axially extending tubular body; an expansion element disposed within the body adapted to expand in response to an increase in the temperature of the probe; a stem slidably mounted in the body and adapted to progress axially in response to expansion of the element; a first seal slidably and sealingly engaged with the body adjacent the stem; a second seal fixedly disposed within the tubular body; and a liquid for occupying voids between the element and the body to ensure that substantially all of the thermal expansion of the element occurs in the axial direction, wherein the expansion element extends between a first end adjacent the first seal and a second end adjacent the second seal.

2. A probe according to claim 1, wherein the stem is axially progressable into opening engagement with an adjacent valve.

3. A probe according to claim 2, wherein the valve is a safety release valve for a hot water system.

4. A probe according to any one of the preceding claims wherein the expansion element includes a precise point expansion wax.

5. A probe according to claim 4 wherein the wax has a breakpoint of about 101 0 C. 10oc 6. A probe according to claim 4 wherein the wax has a breakpoint of about 90 0

C.

7. A probe according to any one of the preceding claims wherein the liquid is a mineral oil based heat transfer media.

8. A probe according to claim 7 wherein the media and the wax are oo° substantially immiscible.

9. A method for manufacturing a temperature probe including the steps of: inserting a first seal into an axially extending tubular body for sealingly engaging against the inner surface of the body; inserting an expansion element having a first end and a second end into the body whereby the first end is adjacent to the first seal; inserting a liquid into the body whereby the liquid is disposed radially between 2 the element and the body; [R:\LIBLL07884.doc:MFF:DMB

Claims (3)

11. A method according to claim 11 wherein the second seal abuts both the 0o liquid and the second end prior to sealing against the body.

12. A temperature probe substantially as hereinbefore described with reference to the accompanying drawings.

13. A method for manufacturing a temperature probe substantially as hereinbefore described with reference to the accompanying drawings. DATED this Twenty-third Day of June, 1999 James Hardie Research Pty Limited Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON [R:\LIBLL]07884.doc:MFF:DMB ABSTRACT A temperature probe includes an axially extending tubular copied body (2) extending between two open ends A cylindrical wax expansion element is disposed within body for expanding in response to an increase in temperature of the probe. A liquid fills the voids between element and body to ensure that substantially all the thermal expansion of the element occurs in the axial direction.