GB2348965A - Method and apparatus for detecting leaks - Google Patents

Abstract

Apparatus is provided for detecting leaks at the joint between a tubular member 1 and another member 3 which may be the cylinder head of a vehicle engine, the apparatus comprising a hollow plunger 5 for inserting into the open end of the tubular member 1 and having at its free end a stop member 6 for bearing up against the closed end of the tube 1 and a sleeve member 8 slideably moveable with respect to the stop member in an axial direction relative to the major axis of the tube, and between each of which stop member and sleeve member are elastomeric sealing means 11 in the form of an O ring seal so that when the sleeve member 8 is moved axially towards the stop member 6 the seal is squeezed in an axial direction such that it expands radially to seal the inside of the tube. A conduit 14 is provided in the stop member for introducing fluid under pressure into that portion of the tube closed by the sealing means such that upon the detection of a drop in fluid pressure the presence of a leak can be detected. The invention also extends to a method of detecting a leak at a joint between a tubular member and another member such as a cylinder head of a vehicle engine which utilises the apparatus of the invention.

Description

Method and Apparatus for Detecting Leaks This invention relates to a method and apparatus for detecting leaks in metal tubes which are typically press fitted to another member with the intention that the joint therebetween is either pneumatically or hydraulically sealed.

In conventional vehicle engine design it is known to press fit steel tubes directly onto cylinder heads to protect spark or ignition plugs from contamination from oil etc. used to lubricate camshaft driven valves, such that it is necessary to test that the junction between each tube and the respective bore within which it is press fitted on the cylinder head is sealed. To achieve this, pressurised air is introduced into the tube from its open end before the spark plug is secured in place, meaning that, necessarily, the open end of the tube has to be pneumatically sealed as well as the threaded bore into which the spark plug is to be introduced prior to pressure testing for possible leaks, either in the tube itself or at the joint with the cylinder head.

This type of pressure test has conventionally been achieved by means of a long hollow plunger which is introduced into the open end of the tube which includes at the free end thereof an annular plug having an elastomeric seal to be pressed around the periphery of the threaded bore into which the spark, plug is to be fitted, thereby sealing the lower end of the chamber created by the tube when press fitted to the cylinder head. In addition, an annular plug at the other end of the plunger has a correspondingly shaped elastomeric seal to thereby sealingly engage the outer rim of the tube, whereafter air can be introduced under pressure through the plunger between these two sealing plugs. Once the air pressure has stabilised within the chamber formed by the sealing plugs and the tube itself, any drop in pressure can thereafter be detected to indicate whether the joint between the tube and the cylinder head has a leak.

There are several disadvantages with this arrangement, one being that although only the joint between the tube and the cylinder head needs to be leak tested, nevertheless the whole of the tube effectively has to be sealed in order to receive a charge of air under pressure. This can be time consuming and by the time that the relatively large charge of pressurised air has stabilised sufficiently to allow a leak test to be carried out with reference to any drop in pressure thereafter, followed by decompression and subsequent withdrawal of the hollow plunger from the tube, a total leak test time of 30 seconds is typical for this kind of operation.

Another disadvantage is that the hollow plunger and its attendant sealing plugs generally have to fit very precisely over and/or around, respectively, the bore for receiving the spark plug and the exposed outer rim of the free end of the tube. Because of this, the apparatus for introducing the hollow plunger into the bore has to be very accurately aligned with it. The depth of penetration must also be closely controlled so as to be not too deep, thereby risking buckling of the tube and/or damage to the hollow plunger and its respective seals, and not too short since otherwise leakage of pressurised air introduced into the bore via the hollow plunger may result, thereby leading to an incorrect pressure test result which could mean, for example, that a leak is detected when one is not present. In addition, it will be apparent that because the free end of the tube is relatively thin the elastomeric seal used to seal the gap between the rim and the respective annular sealing plug can wear out relatively rapidly, requiring frequent replacement.

It is an object of the present invention to provide apparatus and a method for carrying out a leak test in a tube fitted to another member, such as to a cylinder head of a vehicle engine, in which the aforementioned disadvantages are obviated.

According to a first embodiment of the invention there is provided leak detecting apparatus for carrying out a leak test on a joint between a tubular member and another member to which it is connected, such as a cylinder head, the apparatus comprising a fluid pressurisable hollow plunger having a free end for inserting into the open end of the tube remote from the said other member, the plunger having a stop member at its free end and a sleeve member slideably moveable with respect to the stop member in an axial direction relative to the major axis of the tube, and elastomeric sealing means between the stop member and the sleeve member for sealing an intermediate portion of the tube when the stop member and the sleeve member are moved relatively towards each other sufficient to press the sealing means against the inside of the tube, and a conduit in the stop member for introducing fluid under pressure into the portion of the tube closed by the sealing means, and fluid pressure drop detection means for detecting a drop in fluid pressure thereafter thereby to indicate the presence of a leak between the connection between the tubular member and the said other member.

Hereafter, the term"intermediate portion of the tube"means any diametrically complete portion not at either end of the tube.

Preferably, the outer diameter of the stop member and sleeve member closely corresponds to the internal diameter of the tube in the region of the sealing means. Conveniently, where the stop member is intended to bear up against the said other member in the region of the joint with the tube the stop member includes a chamfered, bevelled or hollowed portion, out of part of which portion terminates the conduit, thereby defining a small pressurisable chamber around the joint to be leak tested when the stop member bears against the said other member within the tube.

Conveniently, the stop member includes on the end remote from the sleeve member a further seal which may suitably be an annular seal for sealing around the rim of a threaded bore of a cylinder head into which a spark plug is to be introduced such that, in contrast to the conventional practice of sealing both ends of the tube and introducing a relatively large charge of air under pressure, with this arrangement only that part of the chamber defined by the tube and the cylinder head at the joint and sealing means of the invention need then be tested for leaks, thereby minimising the volume of air required in order to carry out a leak test.

Preferably, the sealing means between the inner and outer member is an O ring seal mounted on a spigot portion of the stop member onto which the sleeve member may be slideably moved theretowards such that the O ring seal may be squeezed in an axial direction relative to the orientation of the major axis of the tube, thereby to expand radially outwardly to form a seal around the inside surface of an intermediate portion of the tube.

According to a second embodiment of the invention there is provided a method of leak testing a tubular member connected to another member, the method comprising the steps of inserting into the open end of the tube a hollow plunger of the type described in the first embodiment of the invention, moving the stop member and the sleeve member of the apparatus relatively towards each other to thereby press the sealing means against the inside of the tube to thereby prevent or inhibit escape of fluid introduced into the closed end of the tube out of the open end thereof, thereafter introducing fluid into the closed end of the tube and measuring any drop in pressure, thereby to determine the presence of a leak in the joint between the tube and the said other member.

The invention will now be described, by way of example only, with reference to the accompanying drawing which schematically shows in part section a hollow plunger inserted within a tube to be tested which, in turn, has been press fitted into part of a cylinder head, only part of which is shown for clarity.

In the drawing a metal tube 1 is shown press fitted into a correspondingly shaped bore 2 within a cylinder head 3 (only part of which is shown) of an internal combustion engine of the type in which a mixture of fuel and air is ignited from a spark plug (not shown) to be fitted within a threaded bore 4 in a conventional manner. To test for leaks in the joint defined by the lower end I b of the tube 1 and the bore 2 of the cylinder head 3 leak testing apparatus in accordance with the invention includes a hollow plunger shown generally at 5 introduced into the open upper end 1 a of the tube 1 and comprises a hollow stop member 6 of external diameter generally corresponding to the internal diameter of the tube 1 pneumatically connected to a supply pipe 7 through which fluid, typically air, can be supplied under pressure, and a sleeve member 8 slideably mounted over the supply pipe 7.

The sleeve member 8 has a flanged annular lower end 9 of external diameter corresponding to that of the stop member 6, which is slideably mounted on a spigot 10 on that part of the stop member 6 remote from the bore 2 in the cylinder head 3 so that the stop and sleeve members 6,8 are slideably moveable with respect to each other along the longitudinal axis of the tube 1.

On a shoulder portion 11 of the spigot 10 is mounted sealing means in the form of an O ring seal 12 which may be expanded radially with respect to the longitudinal axis of the tube 1 by being compressed between the flanged lower end 9 of the sleeve member 8 and the shoulder portion 11 of the stop member 6 when the former is moved downwards towards the closed end lb of the tube 1 beyond the limit of movement permitted by the stop member 6 within the shaped bore 2 of the cylinder head 3 in a manner to be described. An annular seal 13 is mounted on the free end of the stop member 6 and,. in use, is used to seal the opening in the cylinder head 3 afforded by the threaded bore 4 for receiving a spark plug (not shown).

The stop member 6 includes a conduit 14 centrally therethrough having an open end 15 through which air under pressure may be forced into that part of the tube 1 between annular seals 12, 13. Around the periphery of the stop member 6 in the region of the open end 15 of the conduit 14 is a chamfered portion 17 forming, in part, a chamber for receiving such a charge of air under pressure.

The upper end of the sleeve member 8 remote from the flanged end 9 is provided with a flange 18 for connecting to a collar 19 by which it may be pneumatically connected to a pressurised air supply shown generally at 20 and secured thereto by threaded bolts 21, only one of which is shown.

In operation, the plunger 5 is introduced into the open end la of the tube 1 to the position shown in which position the annular seal 13 at the free end of the stop member 6 is in abutment with the cylinder head 3 around the periphery of the threaded bore 4, whereafter the sleeve member 8 is pressed downwards sufficient to enable the O ring seal 12 to become compressed between the shoulder portion 11 and the flanged end 9 so as to cause it to expand radially and thereby sealingly engage with the inner surface of the tube 1. When this happens that part of the stop member 6 between the 0 ring seal 12 and annular seal 13 is effectively pneumatically sealed apart from the conduit 14 such that upon subsequent introduction of pressurised air via supply pipe 7 and conduit 14 into the closed end 1 b of the tube 1 in the region where it is press fitted into the bore 2 of the cylinder head 3 a leak test can then be carried out.

It will be appreciated that although only a relatively small amount of air is then occupying any voids between the chamfered portion 17 of the stop member 6 and the inside surfaces of the lower end of the tube lb and adjacent surfaces of the cylinder head 3, nevertheless if a leak is present this can then be readily detected by monitoring any pressure drop in the air supplied via the conduit 14 such that the apparatus can be used to detect leaks therein using only a small supply of pressurized air relative to conventional practice. Because only a very small amount of air is required to do this, the time taken for carrying out the leak test is commensurately shorter than through the use of conventional apparatus which would normally require air to be pumped under pressure into the whole of the inside of the tube 1 and, following a pause to allow the air to stabilise, a leak test then carried out.

In contrast, because only a relatively small volume of pressurised air is used in accordance with the invention, stabilisation time is commensurately shorter, as is also decompression time. Cost savings can also be achieved because of the need to only supply a relatively small volume of pressurised air. In addition, because the free end of the stop member 6 is chamfered it will be further understood that the plunger 5 essentially centralises itself within the bore of the tube 1 in contrast to the need in conventional practice to carefully align the annular seal around the rim of the open end of the tube. A particularly advantageous feature of the invention over the prior art is that the apparatus is able to test joints in bores of varying lengths so that it is no longer necessary to provide multiple sets of plungers for sealing varying lengths of tube having a common bore diameter.

The invention therefore provides an elegant solution to a number of problems and although the invention has been described primarily with reference to use with a tube press fitted to a cylinder head of a vehicle engine nevertheless it will be apparent that it can be readily adapted to test joints between tubes and other members, which may even be closed members, without departing from the spirit or scope of the invention.

Claims (9)

1. Claims 1. Leak detecting apparatus for carrying out a leak test on a joint between a tubular member and another member to which it is connected, such as a cylinder head of an engine, the apparatus comprising a fluid pressurisable hollow plunger having a free end for inserting into the open end of the tube remote from the said other member, the plunger having a stop member at its free end, a sleeve member slideably moveable with respect to the stop member in an axial direction relative to the major axis of the tube, and elastomeric sealing means between the stop member and the sleeve member for sealing an intermediate portion of the tube when the stop member and the sleeve member are moved relatively towards each other sufficient to press the sealing means against the inside of the tube, and a conduit in the stop member for introducing fluid under pressure into the portion of the tube closed by the sealing means, and fluid pressure drop detection means for detecting a drop in fluid pressure thereafter thereby to indicate the presence of a leak at the connection between the tubular member and the said other member.
2. 2. Leak detecting apparatus according to Claim 1 in which the outer diameter of the stop member and sleeve member closely corresponds to the internal diameter of the tube in the region of the sealing means.
3. 3. Leak detecting apparatus according to Claim 2 in which the stop member includes a chamfered, bevelled or hollowed portion, out of part of which portion terminates the conduit.
4. 4. Leak detecting apparatus according to Claim 2 or Claim 3 in which the stop member includes on the end remote from the sleeve member a further seal.
5. 5. Leak detecting apparatus according to Claim 4 in which the further seal is an annular seal adapted to seal the rim of a threaded bore of a cylinder head of a vehicle engine.
6. 6. Leak detecting apparatus according to any preceding Claim in which the sealing means between the inner and outer member is an O ring seal mounted on a spigot portion of the stop member onto which the sleeve member may be slideably moved theretowards such that the O ring seal may be squeezed in an axial direction relative to the orientation of the major axis of the tube, thereby to expand radially outwardly to form a seal around the inside surface of an intermediate portion of the tube.
7. 7. A method of leak testing a tubular member connected to another member, the method comprising the steps of inserting into the open end of the tube a hollow plunger of the type described in any one of Claims 1 to 6, moving the stop member and the sleeve member of the apparatus relatively towards each other to thereby press the sealing means against the inside of the tube to thereby prevent or inhibit escape of fluid introduced into the closed end of the tube out of the open end thereof, thereafter introducing fluid into the closed end of the tube and measuring any drop in pressure, thereby to determine the presence of a leak at the joint between the tube and the said other member.
8. 8. Leak detecting apparatus substantially as hereinbefore described.
9. 9. A method of leak testing substantially as hereinbefore described.