GB2050841A - Enclosure apparatus, such as medical isolator - Google Patents

Abstract

The invention relates to enclosure apparatus comprising a flexible enclosure envelope (9) in which human or animal patients may be kept in a positive or negative pressure environment isolated from the ambient environment, this environment being provided by blowing air, by means of blowing section (3), through a pipe (7) into the envelope (9) and exhausting it, with exhausting section (1), through a further pipe (5) into the atmosphere. A control device (10, 11) controls the state of a flow regulating device (12) in one of the pipes (7, 5) in response to changes in position of a flexible wall portion of the envelope, so as to tend to maintain a substantially constant air pressure inside the envelope. In order to keep the air pressure substantially constant even in the case of a large hole (for example) developing in the envelope wall, the position of the flexible wall portion changing by more than a predetermined amount is detected, for example by means of a microswitch (15), to cause a control valve (14) in pipe (7) (negative pressure environment) or pipe (5) (positive pressure environment) to close at least partially. <IMAGE>

Description

SPECIFICATION Enclosure apparatus This invention relates to enclosure apparatus, such as for example a medical isolator in which human or animal patients may be kept in a positive or negative pressure environment isolated from the ambient environment.

An isolator usually comprises a thin-walled flexible envelope of transparent plastics material in which the appropriate isolated environment is maintained. Occasionally, owing to an accident for example, the enclosure envelope can become torn and this in turn will upset the established pressure within the isolated environment, with possible risk of infection to the patient (in the case of a positive pressure isolator) or to the attendant personnel (in the case of a negative pressure isolator). To safeguard against such risks, appropriate measures need to be taken. One known way of dealing with the difficulty is shown in Figure 1 where, by way of example, a negative pressure isolator is shown. As can be seen, the enclosure envelope, denoted by reference numberal 9 and shown very diagrammatically in Figure 1, is provided with an air supply pipe 7 and an exhaust pipe 5.The negative pressure environment is maintained within the envelope 9 by drawing in air and blowing it, by means of blowing section 3, along the pipe 7, through an input filter 8, into the envelope 9 and simultaneously exhausting air from the envelope, via an outlet filter 2 and the exhaust pipe 5, by means of an exhausting section 1, from where the air is exhausted to atmosphere. The blowing and exhausting sections are powered by a single motor so that neither section can be operated without the other. The difference between the delivery pressure of the blowing section 3 and the suction pressure established at the upstream side of the exhausting section controls the negative pressure in the isolator envelope while the speed at which the blowing and exhausting sections are operating governs the maximum flow rate through the envelope.A restrictor valve 4 can be used for adjusting the flow rate through the isolator envelope.

In use, changes in envelope pressure occur due to factors such as changes in flow rate when the restrictor valve 4 is adjusted, or the filters 2, 8 becoming gradually blocked with dust, or, possibly, a small leak in the envelope wall, or small displacements of air caused by, for example, manipulations carried out within the enclosure envelope with the use of gloves suitably attached in airtight fashion within openings formed in the wall of the enclosure envelope.In order to restore the envelope pressure to a substantially constant value, e.g. typically at a pressure of 4 mm of water below ambient pressure, irrespective of such factors, an automatic servosystem is used which comprises a balance arm 10 pivoting about a stationary pivot 13, with one end attached to a flexible wall portion of the envelope 9 and the other end of which is connected to an adjustable restrictor valve 12 in the exhaust pipe 5 by means of a cord 11. Any change in position of the wall portion of the envelope to which the balance arm is attached, brought about by a change in pressure in the enclosure envelope due to a small tear or the like, will cause the arm to adjust the setting of the restrictor valve so as to tend to restore the enclosure pressure to its former value.The shortcoming with this system is that in the event of, for example, a large hole developing in the envelope, even with the restrictor valve adjusted to its fully open position by the balance arm, it may be impossible to restore the envelope pressure sufficiently closely to the required value.

According to the invention there is provided enclosure apparatus comprising an enclosure envelope, first and second pipes for supplying gas to the envelope and exhausting gas from the envelope, respective fan means in the first and second pipes for maintaining the flows of gas therein so as to sustain a positive or negative pressure environment in said envelope, a flow regulating device in one of the pipes, a control device, including a sensing element responsive to changes in position of a flexible wall portion of the envelope brought about by pressure changes therein, arranged to control the state ofthe regulating device continuously, in response to changes in position in said wall portion, such as to tend to restore the gas pressure in the envelope to a constant positive or negative value, a control valve in said first or second pipe depending upon whether the envelope environment is a negative or positive pressure environment, respectively, and means arranged to effect a closing action of the control valve so as to at least reduce the flow of gas therethrough if the position of said wall portion changes by more than a predetermined amount.

In a preferred arrangement the control device comprises a balance arm pivotally mounted at an intermediate position along its length and connected at one end to the said wall portion and at the other end to the regulating device, and the means arranged to effect a closing action of the control valve comprises a microswitch which is operable to control operation of the control valve and which is positioned to be operated by the balance arm if the position of the said wall portion changes by more than said predetermined amount.

The means arranged to effect a closing action of the control valve may additionally comprise timing means to inhibit its operation unless the position of the said wall portion remains changed by more than said predetermined amount for more than a preset time. Expediently, the control valve is a solenoidoperated butterfly valve and the timing means comprises a delay device connected, between the microswitch and the solenoid of the butterfly valve, in an energisation circuit for said solenoid.

Preferably, the regulating device is in the second pipe. Also, it is desirable for the enclosure apparatus to further comprise an alarm unit operative to provide an alarm if the position of the said wall portion changes by more than said predetermined amount.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to Figure 2 of the accompanying drawings which shows diagrammatically an embodiment of the invention.

Several parts correspond to other parts shown in the Figure 1 enclosure apparatus and where this is the case, identical reference numerals are used.

Thus, it is not necessary to describe again these parts ofthe apparatus. As shown, however, the enclosure apparatus additionally incorporates a solenoid-operated butterfly valve 14 connected in the supply pipe 7. Under normal operating condi tions,the solenoid is not energised and the valve remains fully open, any small changes in pressure within the envelope 9 being counter-balanced by the operation of the balance arm 10.If, for example, a substantial leak develops in the envelope wall and the required negative pressure within the envelope cannot be maintained by the operation ofthe servo-system, the resulting change in position of the portion of the envelope wall to which the balance arm is attached is sufficient to cause the balance arm to operate a microswitch 15 which causes the solenoid of the butterfly valve to be energised with the result that the valve 14 closes to at least reduce, and preferably throttle off completely, the inlet supply pipe. The envelope pressure will then usually be restored to its former level with the assistance of the servo-system. An alarm unit (audible and/or visual) can be arranged so that it will operate if and when the butterfly valve 14 closes.

The system as described is notwholly advantageous in that if, for example, an operator manipulates something within the enclosure envelope so as to displace air and thereby change the air pressure in the isolator environment, the solenoid-operated butterfly valve might open and close several times. To avoid this problem, preferably a delay device is operatively connected, between the microswitch and the solenoid-operated valve, in the energisation circuit of the solenoid so as to prevent the valve from operating unless the microswitch is closed for a minimum period of time. This period, which could typically take the value of approximately four seconds, is so chosen that factors such as manipulations within the enclosure wall will not cause the butterfly valve to operate whereas any sustained leakage, for example, will result in the valve closing to restore as closely as possible the required negative pressure within the enclosure envelope.

The described arrangement is not confined to negative pressure isolators but is equally applicable to a positive pressure arrangement, providing the butterfly valve 13 is then positioned within the suction or exhaust line 5. Irrespective of whether the isolator has a positive or negative pressure envelope, a workable arrangement would be provided by incorporating the regulating valve 12 in the supply line, but in both cases it is preferred that it be in the suction line.

Claims (7)

1. Enclosure apparatus comprising an enclosure envelope, first and second pipes for supplying gas to the envelope and exhausting gas from the envelope, respective fan means in the first and second pipes for maintaining the flows of gas therein so as to sustain a positive or negative pressure environment in said envelope, a flow regulating device in one of the pipes, a control device, including a sensing element responsive to changes in position of a flexible wall portion of the envelope brought about by pressure changes therein, arranged to control the state of the regulating device continuously, in response to changes in position in said wall portion, such as to tend to restore the gas pressure in the envelope to a constant positive or negative value, a control valve in said first or second pipe depending upon whether the envelope environment is a negative or positive pressure environment, respectively, and means arranged to effect a closing action of the control valve so as to at least reduce the flow of gas therethrough if the position of said wall portion changes by more than a predetermined amount.

2. Enclosure apparatus according to claim 1, wherein the control device comprises a balance arm pivotally mounted at an intermediate position along its length and connected at one end to the said wall portion and at the other end of the regulating device, and wherein the means arranged to effect a closing action of the control valve comprises a microswitch which is operable to control operation of the control valve and which is positioned to be operated by the balance arm if the position of the said wall portion changes by more than said predetermined amount.

3. Enclosure apparatus according to claim 1 or2, wherein the means arranged to effect a closing action of the control valve additionally comprises timing means to inhibit its operation unless the position of the said wall portion remains changed by more than said predetermined amount for more than a preset time.

4. Enclosure apparatus according to claim 3 as appended to claim 2, wherein the control valve is a solenoid-operated butterfly valve and the timing means comprises a delay device connected, between the microswitch and the solenoid of the butterfly valve, in an energisation circuit of said solenoid.

5. Enclosure apparatus according to any preceding claim, wherein the regulating device is in the second pipe.

6. Enclosure apparatus according to any preceding claim, further comprising an alarm circuit operative to provide an alarm if the position of the said wall portion changes by more than said predetermined amount.

7. Enclosure apparatus substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.