GB2331156A

GB2331156A - Leak testing in autoclaves

Info

Publication number: GB2331156A
Application number: GB9822583A
Authority: GB
Inventors: Keith Hannant
Original assignee: Smiths Group PLC
Current assignee: Smiths Group PLC
Priority date: 1997-11-08
Filing date: 1998-10-19
Publication date: 1999-05-12
Anticipated expiration: 2018-10-19
Also published as: GB2331156B; GB9822583D0

Abstract

An autoclave control unit 4 tests operation of the autoclave by turning on a pump 10 to evacuate the pressure vessel 1 and then monitors rise in pressure within the vessel to detect any leaks. If the leakage rate is too high the control unit 4 may disable the steriliser, preventing further sterilisation cycles being started until the leak is corrected. The control unit 4 then switches a solenoid valve 14 connected to a needle valve 13 so that a predetermined leak is connected to the vessel 1. The control unit 4 monitors the rise in pressure to determine if this is within predetermined limits and, if it is, it then monitors the output of an air detection system 23 to check if this detects the predetermined leak. The results of the tests are printed by a printer 31.

Description

AUTOCLAVES This invention relates to autoclaves and to methods of testing autoclaves.

Autoclaves, such as autoclave sterilizers, must be tested frequently to ensure safe operation and to check that objects in the autoclave are subject to the desired treatment cycle.

One of the tests involves testing for leaks in the pressure vessels and testing that the autoclave's air detection system is functioning correctly. These tests are carried out by an engineer who evacuates the pressure vessel, using the autoclave vacuum pump, with all connections to the chamber sealed off. The engineer monitors the rise in pressure of the chamber as air enters through any leaks. If the rate of pressure rise is too high, the autoclave fails the test and is returned for servicing. If the autoclave passes this test, the engineer connects a calibrated leak to a port opening into the chamber, while it is still at reduced pressure, and checks if the autoclave's air detection system responds to the leak within a set time. The autoclave passes the test if the air detection system does detect the leak.

Although this testing system is reliable, it requires the presence of a trained engineer and, therefore, adds to the cost of using the autoclave.

It is an object of the present invention to provide an improved autoclave.

According to the present invention there is provided an autoclave including a pressure vessel, a pump for evacuating the pressure vessel, a pressure sensor for monitoring pressure within the pressure vessel, and control means, the control means being operable first to cause the pump to evacuate the vessel, then to seal the vessel, to monitor an output of the pressure sensor and to determine whether the rate of rise of pressure is within predetermined limits so as thereby to check for leaks into the vessel, and the control means being operable to provide a signal indicative of whether leakage into the vessel is within predetermined limits.

The autoclave preferably includes a predetermined leak and means for selectively connecting or isolating the leak from the pressure vessel, the control means being arranged to connect the leak to the vessel after the vessel has been evacuated by the pump and to monitor the output from the pressure sensor to determine whether the rate of rise of pressure is within second predetermined limits, and the control means being arranged to provide a signal indicative of whether the predetermined leak is within the second predetermined limits. The predetermined leak may be a needle valve, the means for selectively connecting or isolating the predetermined leak from the pressure vessel being a solenoid valve, and the control means being connected with the solenoid to control operation thereof. The autoclave preferably includes an air detection system, the control means being operable to connect the predetermined leak to the vessel and to monitor an output from the air detection system to check whether the air detection system detects the predetermined leak, the control means being arranged to provide a signal indicative of whether the air detection system is operating correctly. The output of the air detection system is preferably only monitored if the predetermined leak is within the predetermined limits. The autoclave may include a printer, and signals from the control means may be supplied to the printer to provide a printed representation of autoclave function. The control means may be arranged to disable operation of the autoclave if the control means detects a fault in the autoclave.

An autoclave sterilizer according to the present invention, will now be described, by way of example, with reference to the accompanying drawing, which shows the sterilizer schematically.

The sterilizer has a pressure vessel or chamber 1 with a door 2 through which articles to be sterilized are placed in the chamber. An electrical heating coil 3 at the bottom of the chamber 1 is energized by a control unit 4 to raise the temperature of water 5 and produce steam. When the chamber 1 is sealed, the steam raises the pressure and temperature in the chamber sufficiently for the articles to be sterilized.

The sterilizer also has a vacuum pump 10 connected via a filter 11 and a pipe 12, which opens into the upper end of the chamber 1. Operation of the vacuum pump 10 is controlled by the control unit 4. When the pump 10 is off, it prevents passage of air through the pump. A needle valve 13 with a predetermined, calibrated leak rate is also connected to the pipe 12 at a location between the pump 10 and the filter 11, via a normally-closed solenoid valve 14. The solenoid valve 14 is also connected to the control unit 4.

The control unit 4 includes a timer 20 and receives outputs from various sensors, such as a pressure sensor 21, a temperature sensor 22 and an air detector system 23. The air detector system 23 monitors variations in pressure and temperature with time. In an effective air removal cycle, these values will have a particular process profile. If the parameters are outside particular ranges, this can indicate that air removal has not been effective, so the cycle is aborted. In particular, a minimum vacuum level has to be achieved within a particular time.

If this is achieved, the chamber 1 is sealed and pressure is monitored to detect leakage into the chamber. The water 5 is then heated under vacuum and a second vacuum phase is performed, pressure being monitored to ensure a particular vacuum level is achieved in a particular time. Subsequently, pressure is monitored at a set temperature to determine if there is good correlation with steam table values. Outputs from the control unit 4 are connected to a display panel 30 and a printer 31.

In normal operation, the user places articles 40 to be sterilized, which may be porous, in the sterilizer chamber 1 and closes the door 2. When the user starts the sterilization cycle, the control unit 4 starts the pump 10 so that it evacuates air in the chamber 1, and then stops the pump to seal the chamber before the heating coil 3 is energized. The sterilizer completes the sterilization cycle in the usual way.

The control unit 4 is arranged automatically to perform three different test procedures, as follows.

The first test is a leak test. To do this, the control unit 4 turns on the vacuum pump 10 with the solenoid valve 14 and any other connections to the chamber 1 closed. The pump 10 pulls a vacuum in the chamber 1 of about 1 2kPa absolute. The control unit 4 then monitors the output of the pressure sensor 21 for a pre-set time, between about 2 to 5 minutes, to monitor the rate of leakage into the chamber 1. If the leakage is less than 2kPa/min, the control unit 4 determines that the leak rate is satisfactory and causes the printer 31 to print out a message to indicate a satisfactory result. If the leakage rate is too high, a message is printed indicating this. A waming message may also be displayed on the display panel 30. The control unit 4 could also disable the sterilizer, preventing further sterilization cycles being started until the leak is corrected.

The next test is to test correct operation of the needle valve 13. While the chamber 1 is still at a reduced pressure, the control unit 4 opens the solenoid valve 14 so that air can leak into the chamber via the needle valve 13. The control unit 4 monitors the pressure output from the sensor 21 and thereby monitors the rate of rise of pressure within the chamber 1. The control unit 4 compares this rate of rise against a predetermined range of rates of rise of pressure to determine whether the rate of rise is within the required limits. If the rate of rise is too fast, it indicates that the needle valve 13 is open too far; if the rate of rise is too slow, it indicates that the needle valve is not open sufficiently, or that there is some blockage in the leak path restricting flow.

If the leak rate is outside the prescribed limits, the control unit 4 signals the printer 31 to print an appropriate message advising the user to have the needle valve 13 checked. A warning message may also be displayed on the display panel 30. The control unit 4 could also disable the sterilizer, preventing further sterilization cycles being started until the leak rate of the needle valve 13 is corrected.

If the leak rate is within the prescribed limits, the control unit 4 continues with an air detector function test, to test correct operation of the air detection system 23. In this, the control unit 4 causes the sterilizer to run a standard sterilization cycle and then introduces a small, controlled leak, by opening the solenoid 14 so that air can flow through the, now calibrated and verified, needle valve 13 during a phase when the chamber 1 is below atmospheric pressure. If the air detection system 23 detects the entry of air into the chamber 1, the control unit 40 determines that the sterilizer is functioning satisfactorily and the printer 31 prints out an appropriate message. If no leak is detected, a fault is indicated on the printout.

Because the leak rate of the needle valve 13 is automatically checked in this way, there is no risk of the air detection test being run with an incorrect leak rate. This avoids the need for the presence of an engineer to check correct operation of the air detection system 23.

Claims

CLAIMS 1. An autoclave including a pressure vessel, a pump for evacuating the pressure vessel, a pressure sensor for monitoring pressure within the pressure vessel, and control means, wherein the control means is operable first to cause the pump to evacuate the vessel, then to seal the vessel, to monitor an output of the pressure sensor and to determine whether the rate of rise of pressure is within predetermined limits so as thereby to check for leaks into the vessel, and wherein the control means is operable to provide a signal indicative of whether leakage into the vessel is within predetermined limits.
2. An autoclave according to Claim 1 including a predetermined leak and means for selectively connecting or isolating the leak from the pressure vessel, wherein the control means is arranged to connect the leak to the vessel after the vessel has been evacuated by the pump and to monitor the output from the pressure sensor to determine whether the rate of rise of pressure is within second predetermined limits, and wherein the control means is arranged to provide a signal indicative of whether the predetermined leak is within the second predetermined limits.
3. An autoclave according to Claim 2, wherein the predetermined leak is a needle valve, wherein the means for selectively connecting or isolating the predetermined leak from the pressure vessel is a solenoid valve, and wherein the control means is connected with the solenoid to control operation thereof.
4. An autoclave according to Claim 2 or 3 including an air detection system, wherein the control means is operable to connect the predetermined leak to the vessel and to monitor an output from the air detection system to check whether the air detection system detects the predetermined leak, and wherein the control means is arranged to provide a signal indicative of whether the air detection system is operating correctly.
5. An autoclave according to Claim 4, wherein the output of the air detection system is only monitored if the predetermined leak is within the predetermined limits.
6. An autoclave according to any one of the preceding claims, including a printer, and wherein signals from the control means are supplied to the printer to provide a printed representation of autoclave function.
7. An autoclave according to any one of the preceding claims, wherein the control means is arranged to disable operation of the autoclave if the control means detects a fault in the autoclave.
8. An autoclave substantially as hereinbefore described with reference to the accompanying drawing.
9. Any novel and inventive feature as hereinbefore described.