The designs for temperature chamber ports on the majority of autoclave chambers are fairly basic in general. This basic design can be problematic, inevitably leading to loss of chamber pressure which in turn creates lost production time and in some cases, product loss as well. Thermal Detection’s Probe Entry Gland autoclave fittings can help to ensure that this loss of chamber pressure is minimised, thereby saving your company from experiencing rejected sterilisation cycles.
Chamber / Load Probe Entry Ports
The most common method of mounting these probes is by using a simple, stainless steel compression fitting that, once mounted and positioned, required the cap nut to be tightened. The tightening forces the internal stainless steel ferrule to drive down around the probe sheath or cable, creating a seal that is either metal to cable or metal to metal. In some cases a rubberised olive is used when sealing against a cable jacket, but in the majority of cases this is more of an afterthought, simply because the internal seating arrangement of the compression fitting was not designed for a flexible seal.
Eventually the probe will need to be replaced, and it can only be withdrawn from the outside chamber thanks to the ferrule, now held firmly against the sheath of the probe. So, getting a new probe fitted also means that a new ferrule is required. When carrying out regulatory calibration checks on the temperature probe, a ‘locked on’ ferrule often interferes with the need to completely insert the probe into the calibration hot block.
A number of autoclave manufacturers have attempted to overcome these problematic issues by designing their own arrangements for temperature chamber and load probe entry ports. In most cases these are designed to accommodate several temperature probes, relying on ‘O’ rings in order to create a seal around the stainless steel sheath or cable jacket. While these are an improvement on the traditional compression fitting methods, it remains that there are still weak points that could be improved.
Autoclave Entry Arrangements
The ‘O’ rings sometimes cause problems due to their small size, meaning that they are easily mislaid or damaged. Fitting them on to cables of three to five metres in length is also more time-consuming, which leads to increased down time. They are also difficult to fit onto the cables often regardless of what material they are made from. Silicone rubber is frequently used for this and trying to slide them over a cable jacket made from the same material is not only time-consuming, but laborious as well. Finally, there is the issue of their sealing contact area which is very small. To offer a credible seal there would have to be no imperfections in the cable jacket at the point at which the ‘O’ ring has to seal.
Thermal Detection Ltd decided to overcome these problematic areas by designing and creating adapters that replace the original autoclave manufacturers entry arrangement. The CPF adapter incorporates a sealing gland with a mounting plate designed to mirror that of the autoclave manufacturers’ original mounting arrangement, enabling the component to be exchanged simply and with ease.
The sealing gland itself consists of five component parts:
- Gland body
- Sealant seat
- Cap nut
The Teflon® sealant, sealant seat and follower are provided with up to six in line holes with the sealant seat and follower holes offering a wider tolerance than the Teflon® sealant. This prevents them from ‘snagging’ when moving them along the lengths of up to six probe cables. The Teflon® sealant has a tighter tolerance, but due to its natural lubricating characteristic it is also easy to move along up to six probe cables.
Having fitted all four component parts onto the probe cables, the three internally located components are then inserted into the gland body and the cap nut is mounted onto its thread. As the cap nut is tightened, the follower is forced to move in a longitudinal direction against the sealant. However the sealant seat prevents the sealant from moving longitudinally and the continuing pressure caused by the torqueing of the cap nut forces the sealant to deform. This deformation fills any remaining void within the gland body and around the cable jackets and forms a pressure tight seal.
The Teflon® sealant provides a sealing length of 12.0mm along the cable jacket and so can accommodate slight imperfections in the silicone rubber cable jacket. In reality there is no comparison with the sealing ability of an ‘O’ ring, which has a substantially less cross sectional area to work with and can often be frustrating to fit.
Thanks to the work from Thermal Detection’s modern manufacturing facility in the North East, chamber pressure can be maintained during autoclave production cycles and validation procedures. This leads to maximum efficiency and better time management from a production perspective. It also means that down time is substantially reduced when the time comes to replace a single or several chamber probes.