AREA OF THE INVENTION This invention relates to the area of protective caps for maintaining the apertures in nozzles clear of foreign matter and in particular to a blow off type of protector cap which can be used in most environments.

BACKGROUND TO THE INVENTION Many nozzle type devices are not necessarily used very frequently and consequently are susceptible to the build up of foreign matter inside the nozzles. Typically this may occur when, for example, nozzles used in fire fighting systems are located in areas where such contamination can arise.

It is in fact known for insects such as wasps to build nests in nozzle orifices and also for dust and other matter to build up in these orifices. One solution has been to cap the unused nozzles. One such cap of a synthetic material, which fitted over the mouth of an existing nozzle, was found to deteriorate with time and to permit foreign matter to enter the nozzle.

Another solution was to provide a metal cap which engaged with the exterior of a nozzle by means of an O-ring incorporated in a peripheral groove on the nozzle. This groove cannot be formed during normal machining of the nozzle and necessitates an additional machining operation.

It is therefore inefficient to provide a groove such as this on all nozzles manufactured as, ultimately, only a very small percentage of nozzles are used with nozzle caps.

In order to overcome the above problems a nozzle cap was devised which was manufactured from metal, and therefore had improved strength when compared to plastic, but also was provided with a recess on its inner periphery into which sealing means in the form of an O-ring or the like could be located. By this means a metal cap was provided which fitted firmly over a nozzle tip, and was able to be blown off in use, but did not require any modification of the nozzle in order to function.

There are however problems with introducing non metallic sealing members such as rubber or synthetic O-rings into certain environments. For example in fire environments such sealing mechanisms may break down. Alternatively oils, grease, fuels and cleaning solvents are among many products which can detrimentally alter the performance of the sealing materials.

There are applications where it is desirable to ensure that the aperture is plugged to positively ensure that there can be no entry of material into the nozzle around the sealing member. In some applications, it is desirable to ensure that the sealing member cannot be inadvertently or deliberately removed to leave the nozzle in an unprotected state.

OUTLINE OF THE INVENTION It is an object of this invention to provide a system whereby an effective blow off cap for a nozzle is provided which is substantially free from the problems previously described above.

The invention provides a blow off cap and nozzle system including a nozzle having a tip, with an aperture therethrough, and having a nozzle cap formed from a sealing membrane attached thereto by retaining means that retains and seals the membrane to the nozzle tip while not hindering any projected spray pattern once the nozzle begins to spray.

It is preferred that the sealing membrane is of a metallic foil such as aluminum, copper or the like. It may however be that in some instances a polymer or rubber type material may be chosen.

It is preferred that the retaining means be a ring which is attached to the nozzle by screw means. It is further preferred that the screw means is a screwed thread or similar retention method once the membrane is placed over the nozzle tip. It is also preferred that the membrane be manufactured to a sufficient thickness and strength such that water pressure build up inside the nozzle is enough to ensure that the cap seal fractures appropriately prior to use.

It may also be preferred that a membrane support be provided in the form of a plug device which can be a close fit into the nozzle aperture and which has an outwardly directed, enlarged, portion which prevents the plug passing into the aperture, which plug is held in place by the membrane.

It may further be preferred that the above membrane support be a metallic device of the nozzle parent material or other and that it be a pintle (mushroom) shaped device being located via a stem, which resides in the nozzle orifice, and having a disc attached centrally at an outside end which supports the membrane while the membrane keeps it in place.

It may be further preferred that the retaining means be knurled, to enable hand operation. Alternatively it may be preferred that it have a hexagonal or other shaped portion to enable it to be fitted and replaced by a standard spanner. It may also be preferred that the retaining means have recesses or the like which can only be contacted by a special tool to make the retaining means difficult to remove without use of the special tool. In order that the invention may be more readily understood we shall describe by way of non limiting example a particular embodiment of the invention with reference to the accompanying drawings.

Brief Description of the Drawing Figures Fig. 1 Shows a cross-section through the blow off cap and nozzle assembly; Fig. 2 Shows a cross-section through a nozzle and associated plug; Fig. 3 Shows a diagrammatic representation of a tool to engage with the retaining means;

Description of an Embodiment of the Invention In a preferred embodiment of the invention the nozzle cap assembly 10 of the invention is provided with a metallic sealing membrane or film 20 which covers the tip of the nozzle 30 and is attached to the nozzle tip by means of a specially designed retaining ring 40 that, while not hindering the projected spray pattern once the nozzle begins to spray, retains and seals the membrane to the nozzle tip.

The nozzle in this embodiment of the invention is provided with a portion of its outer periphery which is adapted to engage with the restraining ring. For example the nozzle may be provided with a threaded section 15 such that once the membrane is placed over the nozzle tip the retaining ring can be easily fitted to the nozzle via a screwed thread 45 or similar retention method The membrane itself is manufactured to a particular thickness and strength which is enough to allow pressure build up inside the nozzle, when use is commenced, which is sufficient to ensure fracture and permanent deformation of the membrane such that the spray pattern is not hindered.

The membrane used may be of a metallic foil such as aluminum, copper or similar, although in some instances a polymer or rubber type material may be chosen.

Although the sealing membrane itself may be adequate to form a seal, it may be required in some instances to include a suitable silicon based sealing grease or equivalent inside the nozzle to act as an ancillary sealing and membrane support. This addition may protect the membrane from environmental degradation while the membrane prevents it from dripping out at elevated temperatures or other conditions.

Any of the above arrangements provides a generally metal blow off cap which does not have the problems of previously described blow off caps.

It is also preferred that a membrane support be provided in the form of a plug device 50 which can be a close fit into the nozzle aperture 16 and which has an outwardly directed, enlarged, portion 55 which prevents the plug passing into the aperture 16, which plug is held in place by the membrane 20. This membrane support 50 may be a metallic device of the nozzle parent material or other and preferably be a pintle (mushroom) shaped device being located via a stem 54, which resides in the nozzle aperture 16, and having a disc or cap 55 attached centrally at an outside end which supports the membrane 20 while the membrane keeps it in place.

This outwardly directed mushroom shaped cap 55 is basically smooth so that it is unlikely to cause any rupturing of the membrane during normal use.

When the nozzle is being sealed the plug is located in the aperture, the membrane placed there over, and the retaining means screwed onto the body of the nozzle.

This provides an arrangement where there can be no ingress of material into the aperture through the spray nozzle and the plug is retained in position by the membrane.

When the pressure input to the nozzle is increased the plug is forced outwardly, which in turn causes rupture of the membrane and the head of the plug is of such a size as to ensure that the rupture of the membrane is such as to move the membrane away from the outlet of the nozzle (Figure 2) to cause no interruption in to the nozzle spray. In the invention, while the inner portion of the retaining ring and the threads thereon are still formed to cooperate with the threads on the nozzle itself, the outer portion can take different forms.

In the first of these the retaining means has a knurled outer surface to enable ready grip and to enable it to be hand tightened and removed. In a second form the external surface may be provided with a hexagonal or square form which can cooperate with the required size spanner to enable it to be tightened or removed by the use of such spanner.

In a third preferred form described here the outer surface of the retaining member can be provided with rectangular recesses 44 or the like, which are adapted to be entered by an extension on a special tool 60, which can have a largely open portion 61 , which has a diameter corresponding closely to that of the nozzle, and which can surround a portion of the nozzle with at least one extension 62 entering one of the recesses 44 and providing a point against which leverage by the tool can be applied.

Once the retaining means is tightened then it is not possible to readily remove this by hand or normal tools, although it is straight forward to remove it by way of the special tool. This embodiment of the invention is preferred to prevent deliberate or accidental tampering. While one example of atamperproof tool has been described here it is envisaged that any combination of recesses or lugs in either the retaining ring or associated tool could be provided.

While we have described herein one particular embodiment of the invention it is to be understood that variations and modifications in the materials used and the features described can still lie within the scope of the invention.