GB2108670A

GB2108670A - Pressure indicators

Info

Publication number: GB2108670A
Application number: GB08230210A
Authority: GB
Inventors: Geoffrey Robinson; Jerry Alan Partington
Original assignee: Prestige Group UK PLC
Current assignee: Prestige Group UK PLC
Priority date: 1981-11-04
Filing date: 1982-10-22
Publication date: 1983-05-18
Also published as: GB2108670B

Abstract

A pressure indicator particularly for a pressure cooker comprises at least one piston (10, 14) capable of restricted movement within a housing (6). One or more dead weight resistances (19, 21) limit the movement of the piston(s) under pressure such that the indicator can indicate a number of distinct changes of the position of the piston(s) relative to the housing at several predetermined pressures. <IMAGE>

Description

SPECIFICATION Pressure indicators This invention relates to pressure indicators.

More particularly the invention relates to pressure indicators for pressure vessels, particularly pressure cookers.

Pressure cookers of the domestic type generally have an escape port in the cover and the pressure within the cooker is regulated by a valve controlling the port. A common type of valve comprises a weight valve designed so that when the pressure cooker and its contents are heated, pressure within the vessel builds up until the internal pressure is sufficient to overcome the weight valve, at which time the weight valve opens so releasing gases (e.g. steam) and controlling the pressure within the vessel.

Control of pressure within the cooker requires careful regulation of the heat input once cooking pressure has been reached to keep the weight valve just discharging steam and so ensure that adequate cooking pressure is maintained. Once cooking pressure has been attained it would be satisfactory to apply only sufficient heat to maintain the internal pressure near the nominal cooking pressure. Excess heat input results in excessive discharge of steam from the valve and hence waste of fuel and loss of water from the contents of the vessel.

Hence it is desirable that the pressure cooker should incorporate a pressure indicator that is of sufficient sensitivity to indicate the pressure within the vessel at cooking pressures. The prior art pressure indicating devices of the spring loaded plunger type, such as that of U.K. Patent Specification 619002, are designed to indicate a gradual change in pressure rather than a number of distinct changes at predetermined pressures. In addition they tend to be inaccurate and have a narrow indicating range. Hence they are not very suitable for the use mentioned above.

Accordingly, a first aspect of the present invention provides a pressure indicator comprising a housing containing a piston capable of restricted movement under pressure, indicating means for indicating the position of the piston relative to the housing, a dead weight resistance for limiting the movement of the piston under pressure, the piston and resistance being so arranged that a first predetermined pressure can cause movement of the piston to a first position and further movement of the piston can occur when the dead weight resistance is overcome at a second predetermined pressure, the second predetermined pressure being higher than the first.

When the pressure indicator of the first aspect is employed on a domestic pressure cooker it is preferred that the piston is arranged (e.g. the weight and dimensions of the piston are chosen) so that the first predetermined pressure is about 0.9 Bar, which is the lower limit of the pressure cooking range. Thus when this pressure is reached the piston moves indicating to the user that the vessel is at cooking pressure. If further heat is applied to the vessel and the pressure exceeds the second predetermined pressure, e.g. about 1.0 Bar, the dead weight resistance is overcome and the piston moves further indicating to the user that the heat input can be reduced.

In a preferred embodiment of the first aspect of the invention, there is a port in the indicator which, in use, provides a communication between the interior of the pressure vessel and the atmosphere. A further piston capable of restricted movement under pressure is arranged so that at a predetermined pressure, lower than the first predetermined pressure, the further piston is capable of movement to close the port in the indicator. The axis of one of the pistons may be arranged within the other. Preferably when used on a domestic pressure cooker the further piston is arranged to close the port at pressures of about 0.04 Bar or less.The port in the pressure indicator can act as an air bleed i.e. when the pressure vessel is heated excess air will be driven out of the vessel through the port but as soon as the vessel reaches the predetermined pressure of about 0.04 Bar the port will be closed so that the vessel can be brought to cooking pressure.

A pressure indicator according to the first aspect of the invention can, for example, indicate to the user that a satisfactory cooking pressure has been reached. However, it is also desirable that the indicator should be capable of indicating lower pressures so that the user can see when the pressure within the vessel is sufficiently low for the vessel to be safely opened.

Accordingly, a second aspect of the invention provides a pressure indicator comprising a housing containing a first piston capable of restricted movement under pressure, a second piston arranged for axial movement in the first piston, indicating means for indicating the position of one or both pistons relative to the housing, a plurality of dead weight resistances for limiting the movement of the pistons under pressure, the pistons and resistances being so arranged that a first predetermined pressure can cause movement of the first and second pistons to a first position, further movement of the second piston can occur when a resistance is overcome at a second predetermined pressure, the second predetermined pressure being higher than the first, and still further movement of the second piston can occur when a further resistance is overcome at a third predetermined pressure, the third predetermined pressure being higher than the second.

Preferably when the second aspect of the invention is in use on a domestic pressure cooker the resistances are so arranged that at pressures of about 0.04 Bar and above the first and second pistons move to the first position indicating to the user that the vessel is under pressure and no attempt should be made to open the vessel. If desired, when in the first position (and in any of the other positions corresponding to higher pressures) one of the pistons, preferably the first piston, can be arranged to interact with a locking mechanism so preventing relative movement of the cover and body of the pressure cooker when the internal pressure is about 0.04 Bar or above.

Also, the first piston may be arranged so that at a pressure below the first predetermined pressure (e.g. at or below 0.04 Bar) it closes a port in the pressure indicator. The port can function as an air bleed the function of which is explained more fully hereinabove in connection with the first aspect of the invention.

The presence of the pistons in the first position indicates to the user that the pressure within the vessel has not reached cooking pressure and further input is required to ensure cooking. The second predetermined pressure can be, for example, about 0.90 Bar, which is the cooking pressure. When the pressure within the vessel reaches this pressure the dead weight resistance is overcome and the second piston moves further indicating to the user that the vessel is at cooking pressure. If further heat is applied to the vessel and the pressure exceeds, for example, about 1.0 Bar, a further resistance is overcome and the second piston moves even further indicating to the user that the heat input can be reduced.The indicating means for indicating the position of the piston or pistons relative to the housing may comprise, for example, markings or other indications on the piston(s) and/or housing or the piston or pistons may, for example, operate another co-operating member and the position of the other member relative to the housing can indicate the pressure.

The invention further provides a pressure cooker comprising a pressure indicator according to the invention and a valve for controlling an escape port in the pressure cooker. The valve may be, for example, a weight valve.

An embodiment of the pressure indicator for use with a pressure cooker will now be described by way of example and with reference to the accompanying drawings in which Figure 1 is a perspective view of a pressure cooker incorporating a pressure indicator of the second aspect of the invention; Figure 2 is a cross sectional view of the pressure indicator of Figure 1 mounted on the cover of the pressure cooker; Figure 3 (a) to (d) is a diagrammatic representation of the cross sectional view of the pressure indicator of Figure 2 under various pressure conditions within the pressure cooker; Figure 4 is a cross sectional view of a modification of the pressure indicator according to the first aspect of the invention; Figure 5 is a cross sectional view of a further modification of the pressure indicator according to the first aspect of the invention.

As shown in Figure 1, a pressure cooker comprises a body portion 1 and a lid portion 2.

Mounted on the lid portion 2 is a conventional weight valve 3, a conventional safety valve 4 and the pressure indicator 5 of the invention. As more clearly shown in Figure 2, the pressure indicator 5 of the second aspect of the invention comprises a housing 6 having a lower screw threaded portion. The housing is held within a hole in the lid 2 of the pressure cooker 1 by means of a screw threaded nut 7 corresponding to the screw threaded portion of the housing 6. A sealing engagement between the housing 6 and the lid 2 is ensured by means of a pressure seal 8 within a groove in the lower surface of the housing 6. Mounted on a shoulder of the housing 6 is a circular cap 9 having a hole in its upper surface.

The housing 6 has radial channels 23 and an axial central bore 24 in which is disposed a piston 10. The lower end of the piston 10 is provided with an enlarged head 11 of diameter greater than that of the bore 24 in the housing 6. Mounted on top of the enlarged portion 11 is a circular sealing ring 1 2. The upper end of the piston 10 is provided with a groove within which is a ring 13.

The piston 10 has a central bore in which is disposed a further piston 14 of small crosssectional area. The piston 14 comprises a narrow shank portion 15 of cross sectional area only slightly less than that of the bore in the piston 10 and an enlarged head portion 16. The head portion 1 6 is provided with a groove near its lower end and held within the groove is a ring 17.

Mounted on top of the enlarged head portion 1 6 is an indicator member 1 8 having a depending skirt portion bearing indication markings (e.g. a coloured band) on its outer surface.

Standing on a lower horizontal ledge of the housing 6 is circular weight member 1 9 which is H-shaped in cross-section and having a central bore for the enlarged head 1 6 of piston 14. The outer surface of upper limbs of the H of the weight member 19 are provided with two bands of indication markings (e.g. an upper band of one colour and a lower band of a different colour). The lower limbs of the H-shaped member are provided with a ledge 20. Radial channels 25 extend through the lower limbs of the weight member 1 9.

Also standing on the housing 6 is a ring shaped weight member 21 having an inwardly directed ledge 22.

The combined weight of the indicator member 18, the weight member 1 9 and piston 14 is designed, relative to the diameter of the piston 14, to be such that the weight member 1 9 can be lifted by a pressure of about 0.9 Bar and the additional weight of the weight member 21 is designed so that the weight member 21 is lifted when the pressure reaches about 1.0 Bar.

In use, when the pressure cooker is unpressurised or the pressure is below 0.04 Bar the indicator 5 is in the position shown in Figure 2 or diagrammatically in Figure 3a. The piston 10 is held in position by contact of ring 1 3 with the housing 6 and piston 14 is held in position by contact of the bottom surface of the enlarged head 16 with the top surface of the piston 10. In this position no indications are visible above the upper surface of the cap 9 indicating to the user that the vessel is unpressurised or under sufficiently low pressure for the lid portion to be removed from the body portion of the pressure cooker.

When the pressure within the vessel is raised air is first vented through the bore 24 in the housing 6 and out through the radial channels 23, 25. At a pressure of 0.04 Bar the indicator takes up the position shown diagrammatically in Figure 3(b). The pressure acts upon the two pistons 10 and 14 to raise them from the initial position.

Piston 10 is forced upwards until its enlarged head 11 and accompanying sealing ring 12 contacts the lower face of the housing 6, thus preventing any further upward movement of piston 10 and causing sealing of the pressure vessel. Upward movement of piston 14 takes place until the ring 1 7 on the head portion 16 contacts the lower surface of the weight 1 9. The - upward movement of the piston 14 takes with it the indicator member 1 8 so that the indications on the outer surface of its depending skirt portion become visible. This indicates to the user that the vessel is pressurised and should not be opened.

However the weight member 1 9 has not risen indicating to the user that cooking pressure has not been attained.

Any further increase in pressure above 0.04 Bar cannot cause further upward movement of piston 14 until the resistance caused by weight member 1 9 is overcome. This takes place when the internal pressure is about 0.9 Bar and the indicator then takes up the position shown diagrammatically in Figure 3(c). In this position, piston 14 has overcome the resistance of weight member 1 9 and the piston 14, together with the attached indicating member 18, has been forced further upwards carrying with it the weight 1 9 resting on the ring 1 7. The upward movement of the weight member 19 is stopped when ledge 20 of weight member 19 contacts ledge 22 of weight 21.In the position indicated in Figure 3(c), the indications on the skirt of indicating member 18 and the first band of indications on the upper limbs of weight member 1 9 are visible to the user indicating that cooking pressure has been attained.

If heat input is continued the pressure within the vessel will continue to rise but no further upward movement of the components can take place until the resistance of the combined weights of the indicating member 1 8, the weight members 19, 21 and piston 14 is overcome and the indicator takes up the position shown diagrammatically in Figure 3(d). This occurs when the internal pressure reaches about 1.0 Bar. In this position, upward travel of piston 14 with accompanying indicator member 18 and weight 1 9 has continued and the upward travel of the weight 19 has carried with it the weight 21. The upward travel can continue until the weight 21 contacts the under surface of the cap 9.In the position illustrated the indications on the skirt of indicating member 1 8 as well as both the upper and lower bands on the upper limbs of weight member 1 9 are visible to the user. This indicates that the pressure within the vessel is above that necessary for pressure cooking and therefore that the heat input can be reduced.

In a falling pressure situation e.g. after cooking pressure has been attained and the heat input then reduced or the conventional valve has been discharged, the indicator would show that the heat input should be increased (if the cooking time had not been completed).

In use the pressure indicator of the embodiment changes position in positive discrete steps indicating in a simple manner to the user the pressure within the cooker even when there is no visible or audible evidence from the conventional weight valve.

The modification shown in Figure 4 is a simplified version of the embodiment shown in Figure 2. Similar members in the two embodiments are given corresponding reference numbers. The embodiment of Figure 4 has no piston corresponding to that of reference 10 of Figure 2 and the piston 14 and the weight member 1 9 are combined into a single member comprising piston 14' having an enlarged head portion 26.

The head portion 26 is provided with a shoulder 27 and indication markings 28, 28' on its surface.

The weight of the piston 14' is chosen so that it is only raised by pressures above about 0.9 Bar.

Thus in use on a pressure cooker the indicator will be in the position illustrated in Figure 4 until the pressure reaches about 0.9 Bar. At this pressure the piston 14' will move upward and the top indications 28 will be visible to the user indicating cooking pressure has been attained. The piston 14' moves upwards until the shoulder 27 contacts the weight 21. If pressure within the vessel is increased the resistance of the dead weight 21 will be overcome at about 1.0 Bar and the lower indications 28' will be visible, indicating that the heat input can be reduced.

The modification shown in Figure 5 is similar to that of Figure 2 except that no provision is made for indicating when the cooker is pressured at low pressures (e.g. pressures of 0.04 Bar and above).

At these low pressures the piston 10" acts as an air bleed in a similar manner to the piston 10 of Figure 2. At higher pressures the piston 14" and the weight member 19" act together as the piston 14' with the enlarged head 26 of Figure 4. Thus when the cooking pressure (e.g. about 0.9 Bar) is reached the piston 14" and the weight member 19" will move upwards until the weight 21 prevents further upward movement. At higher pressures (e.g. of about 1.0 Bar) the resistance of the weight 21 is overcome and the piston 14" and weight member 19" will move further so exposing further indicator markings on the surface of the weight 1 9".

Claims

1. A pressure indicator comprising a housing containing a piston capable of restricted movement under pressure, indicating means for indicating the position of the piston relative to the housing, a dead weight resistance for limiting the movement of the piston under pressure, the piston and resistance being so arranged that a first predetermined pressure can cause movement of the piston to a first position and further movement of the piston can occur when the dead weight resistance is overcome at a second predetermined pressure, the second predetermined pressure being higher than the first.

2. A pressure indicator comprising a housing containing a first piston capable of restricted movement under pressure, a second piston arranged for axial movement in the first piston, indicating means for indicating the position of one or both pistons relative to the housing, a plurality of dead weight resistances for limiting the movement of the pistons under pressure, the pistons and resistances being so arranged that a first predetermined pressure can cause movement of the first and second pistons to a first position, further movement of the second piston can occur when a resistance is overcome at a second predetermined pressure, the second predetermined pressure being higher than the first, and still further movement of the second piston can occur when a further resistance is overcome at a third predetermined pressure, the third predetermined pressure being higher than the second.

3. A pressure indicator as claimed in claim 1 which incorporates a further piston capable of restricted movement under pressure, the further piston being arranged so that at a predetermined pressure, lower than the first predetermined pressure, the further piston is capable of movement to close a port in the indicator.

4. A pressure indicator as claimed in claim 3 where the axis of one piston is arranged within the other.

5. A pressure indicator as claimed in claim 2 wherein the first piston is arranged so that at a pressure below the first predetermined pressure it is capable of movement to close a port in the indicator.

6. A pressure indicator substantially as hereinbefore described with reference to and as illustrated in any one of the Figures of the accompanying drawings.

7. A pressure cooker comprising a pressure indicator as claimed in any one of the preceding claims and a valve for controlling an escape port in the pressure cooker.