GB2279015A

GB2279015A - Vaporizer flow path

Info

Publication number: GB2279015A
Application number: GB9312212A
Authority: GB
Inventors: John Robert Laybourne; Justin Mott
Original assignee: Blease Medical Equipment Ltd
Current assignee: Blease Medical Equipment Ltd
Priority date: 1993-06-14
Filing date: 1993-06-14
Publication date: 1994-12-21
Also published as: GB9312212D0

Abstract

A vaporizer comprises gas inlet 1 and outlet ports, gas inlet and outlet control means 8, 21 at least one liquid reservoir chamber 11, at least one gas passage 5, and at least one gas vaporization zone 9 the volume of which remains substantially constant throughout the period of operation of the vaporizer and which comprises one or more gas passages substantially surrounded by liquid absorbant material 17, said material 17 being substantially saturated with liquid from the liquid reservoir chamber 11, there being liquid communication means 18 between the liquid absorbant material 17 and the liquid reservoir chamber 11 such that liquid is replenished to said liquid absorbant material 17 as vapour passes therefrom to the gas. The material 17 surrounds a spring 16 both of which are coiled around core 12 of zone 9. Carrier gas passes through a passage formed between spring 16 and member 17 and liquid evaporates from material 17 into the carrier gas in the passage. A flow path restrictor restricts flow of saturated gas exiting zone 9 into chamber 11. <IMAGE>

Description

VAPORIZER FLOW PATH According to the present invention there is provided a vaporizer with a new and improved carrier gas flow path. This vaporizer provides improved control of the volume percentage addition of vapour to the carrier gas during operation of the vaporizer in varying opperative conditions.

Vaporizers are used in a variety of applications. For ease of reference in the following description, the invention will be described in relation to, anaesthetic vaporizers. However, the invention is not limited to these devices.

There are two main types of anaesthetic vaporizer, the Plenum vaporizer and the Draw Over vaporizer and the present invetion applies equally to both.

Anaesthetic vaporizers are usually designed for "out of circuit use" (on the backbar of an anaesthetic machine) in continuous flow techniques of inhalation anaesthesia. They form an integral part of anaesthetic machines and convert the normally liquid anaesthetic agent into a vapour and allow the anaesthetist to determine the percentage of vapour being delivered in a controlled, predictable and safe way.

The modern anaesthetic machine, apart from acting as a mounting platform for anxillary equipment, such as ventilators and patient monitors, is basically designed to deliver a controllable mixture of carrier gases, (such as oxygen, nitrous oxide, air, carbon dioxide, helium etc.), into and through the vaporizer system or backbar. The backbar may be made up of more than one vaporizer. When the carrier gases -pass through a vaporizer which has been switched on, the-vaporizers task is to add the correct volume percentage (vol. %) of anaesthetic agent vapour to the carrier gas. The total gas flow, i.e carrier gas plus the vol. % of anaesthetic agent, then passes to the common gas outlet of the anaesthetic machine.

It is essential that the vaporizer deliver accurate concentrations of anaesthetic agent over a wide range of conditions. Factors which may affect a vaporizer's output performance are temperature changes, flow rate fluctuations and pressure fluctuations.

Current vaporizers are calibrated with the device at certain conditions of temperature, flow rate and level of liquid in the chamber. During routine use, any of the above parameters may change and current devices are designed to accommodate this variance within certain tolerance levels.

During routine use, the liquid in the chamber vaporizes and provides a level of vapour concentration at the liquid/gas interface. If the amount of fresh carrier gas entering the chamber remains constant, this fresh gas picks up vapour during its passage through the chamber before exiting. From the fresh gas inlet port to the gas/liquid interface, a vapour concentration gradient exists. As the liquid evaporates, the level of liquid within the chamber reduces. Thus, the volume of gas within the chamber increases and the amount of vapour required to maintain the level of vapour concentration increases. As the liquid level drops further, the gradient changes. This variation of saturated vapour available for the fresh carrier gas to acquire, means that the calibrated settings produce different actual outputs with changes in the liquid level. This feature is more prominent with higher concentration settings and higher gas flows.

The object of the present invention is to overcome this problem by restricting the flow path of the fresh carrier gas flow to a substantially constant volume, irrespective of the liquid level within the chamber.

According to the present invention there is provided a vaporizer comprising gas inlet and outlet ports, gas inlet and outlet control means, at least one liquid reservoir chamber, at least one gas passage, and at least one gas vaporization zone the volume of which remains substantially constant throughout the period of operation of the vaporizer and which comprises one or more gas passages substantially surrounded by liquid absorbant material said material being substantially saturated with liquid from the liquid reservoir chamber, there being liquid communication means between the liquid absorbant material and the liquid reservoir chamber such that liquid is replenished to said liquid absorbant material as vapour passes therefrom to the gas.

Gas inlet and outlet ports may be any type suitable to enable gas supply to be connected to the inlet port and gas take off to be connected to the outlet port. Their design will be dependant on the nature of the gas supply and take off members to be attached thereto.

Gas inlet control means and gas outlet control means may be any suitable means, examples of which include valves, zero lock ports, gates and the like.

Preferably one or both of the gas inlet and outlet control means are adjustable such that the amount of gas entering and leaving the gas vaporization zone may be adjustable and so that the resistance or back pressure to flow entering the vaporization zone may be adjusted. One example of a valve is a needle valve.

In one embodiment the gas inlet and outlet control means may be jointly controlled by one control such that at least adjustment between the open and closed positions will operate to affect both the inlet and outlet control means at the same time. Alternatively, the inlet and outlet control means may be interlinked so that they may be jointly and severally controlled, for example the outlet control means may be adjustable so as to change the flow of the gas passing it, but when moved to the closed position it interacts with the inlet control means so that both the outlet and inlet control means stop gas flowing into or out of the gas vaporization zone.

The majority, if not all of the vaporization and mixing with the carrier gas, occurs in the gas vaporization zone and more particularly in a vapour supply zone located therein wherein gas passing therethrough picks up vapour. The volume of the vapour supply zone is substantailly constant notwithstanding changes in the liquid level within the liquid reservoir chamber during operation of the vaporizer. Preferably the vapour supply zone comprises one or more cavities.

Preferably said cavities are formed by at least one layer of a permeable liquid absorbant material which material contains the liquid to be vaporized and mixed with the carrier gas. The cavity/s may be any shape or size suitable for the purpose. Gas within the vapour supply zone may pass through one or more layers of the liquid absorbant material as well as through the cavities. Cavities may be formed within the liquid absorband material. In one preferred embodiment the vapour supply zone is formed by a tube comprising liquid absorbant material and the carrier gas passes through the tube cavity in close contact with the surrounding liquid absorbant material.

In another embodiment the cavity/s may contain liquid which vaporizes and is picked up by the carrier gas passing through.

The liquid absorbant material may incorporate or may be supported by one or more support members.

Examples of support members include one or more helically wound spaced components, springs, webb members, perforated tubes, hoops, and the like or any combination of these.

The gas vaporization zone may comprise one or more vapour supply zones each of which may provide vapour to the carrier gas. In the event that more than one vapour supply zone is provided they may be interconnected or may be speced apart with gas passage/s extending there between.

Preferably the gas exiting the vapour supply zone, or last of said zones if more than one are provided, is saturated with vapour. Preferably, substantially all of the gas passing from the vapour supply zone, or last of said zones if more than one are provided, proceeds to the gas outlet control and does not pass into the liquid reservoir chamber.

The liquid reservoir chamber is preferably proximate the gas vaporization zone. The liquid reservoir chamber holds the liquid which throughout any single operation of the vaporizer will be vaporized and mixed with the carrier gas. The vaporizer preferably includes filler means so that liquid within the chamber may be replenished.

There extends between the gas vaporization zone and the liquid reservoir chamber,liquid comunication means such that liquid from the liquid reservoir chamber is supplied to the liquid absorbant material in the gas vaporization zone. The liquid may be transferred from the liquid reservoir chamber to the gas vaporization zone by pumping, gravity feed or other known means. Preferably capillary action supplies the liquid to the liquid absorbant material. Preferably a permeable capillary material extends between the liquid reservoir chamber and the gas vaporization zone such that liquid may travel from the chamber to the liquid absorbant material.

Preferably, the greatest proportion of the vapour saturated gas does not pass into the liquid reservoir chamber. However, some of said gas may pass into the liquid reservoir chamber and may serve to equalize the gas pressure as the liquid level within said chamber changes during operation of the vaporizer. Preferably there is provided a flow path restricter between the gas vaporization zone and the liquid reservoir chamber which restricts the flow of vaporized gas to said chamber. It is further preferred that said flow path restricter comprises at least one layer of liquid absorbant material from which vapour may pass to the gas in event that the gas is not saturated.

In an alternative embodiment of the present invention carrier gas may pass through the liquid reservoir chamber before entering the gas vaporization zone. In this embodiment the carrier gas collects vapour from the liquid reservoir chamber which may or may not lead to saturation of the gas, but the gas then passes through the gas vaporization zone and if the gas remains unsaturated then saturation occurs in the gas vaporization zone.

The saturated gas passes through the vapourizer and is then mixed with by-pass gas in the required proportion to deliver the required percentage of anaesthetic to the patient.

The main chamber and other parts of the vaporizer in contact with anaesthetic liquid other than the liquid absorbant material may be made from stainless steel, Delrin (trade mark, a product of Du Pont) Brass to British standard 2874 standard CZ 132, anodized alluminium, or plastics which do not degrade when exposed to the liquid which is to be vaporized, and the like or any combination of these. The liquid absorbant material may be made of polytetra-fluoroethelene sold as teflon (trade mark) felt, cotton cloth felt, stainless woven mesh, polyethylene, porous plastics, scintered materials and the like or any combination of these.

Wherein the vaporizer of the present invention is a Plenum vaporizer, it includes gas flow rate control means. The gas flow rate control means may comprise a valve or other gas spliting device. In one embodiment the flow rate control means is provided by a by-pass splitting valve. In one form said valve is a needle valve. However, other known devices will be suitable.

Preferably, the flow rate control means cooperates with a temperature compensator such that variations in temperature within the vaporizer will be detected by the temperature compensator which will act on the flow rate control means to adjust the flow rate such that as the temperature in the gas vaporization zone decreases the gas flow rate control means causes an increased proportion of the gas flow to be diverted into the gas vaporization zone.

One embodiment of the present invention is shown in figures 1 and 2. Figure 1 shows a schematic cross-section of one embodiment of a Plenum type anaesthetic vaporizer according to the present invention. Figure 2 is an enlargement of the lower section of the vaporizer shown in figure 1.

In the embodiment shown in figure 1, gas enters inlet port 1 and passes through gas passage 2. Gas passage 2 divides into 2 passages. One portion of gas flows along by-pass passage 3 and the other portion proceeds along inlet passage 5. As shown in figure 1 gas flow rate control means in the form of by-pass valve 4 is located in by-pass passage 3. By-pass valve 4 may be adjustable such that the proportion of gas passing through by-pass passage 3 relative to the proportion of gas passing through inlet passage 5 may be adjusted. By-pass valve 4 is linked to temperature compensator 6. The energy for vaporization is derived from the liquid agent and as the vapour is continually swept away, cooling occurs. This necessitates readjustment of the proportion of gas passing through passages 3 and 5 in order to maintain the delivered partial pressure of the liquid agent to the patient.

Temperature compensator 6 provides this temperature compensation means by interacting with by-pass valve 4 to regulate the relative proportion of gas flowing through passages 3 and 5.

During operation of the vaporizer the major part of the gas stream flows through by-pass passage 3.

this gas stream mixes with vapour saturated carrier gas down stream, that is at gas mixing junction 7.

The carrier gas passing through inlet passage 5 proceeds past inlet control means 8 in the form of a zero lock valve which when open allows gas to flow into gas vaporization zone 9 but when closed stops any gas passing therethrough.

Gas vaporization zone 9 is located proximate liquid reservoir chamber 11.

Gas vaporization zone 9 comprises vapour supply zone 10, core 12, and gas exit passages 14 and 15.

Vapour supply zone 10 comprises a spring 16 which is surrounded by permeable capillary liquid absorbant material 17. Liquid absorbant material surrounds the spring and the carrier gas passes through the cavity formed by the spring and liquid absorbant material. The spring and liquid absorbant material are coiled around core 12 . One end of the spring liquid absorbant material communicates with the gas inlet passage 5 such that gas passes through gas inlet passage 5 and then through the cavity formed by the spring and liquid absorbant material.

The other end opens into gas exit passage 14.

Liquid contained in the liquid absorbant material vaporizes and mixes with the gas flowing through the cavity. The supply of liquid to the liquid absorbant material and length of the vapour supply zone is sufficient that saturation of the gas occurs by the time the gas exits the cavity into gas exit passage 14. The saturated gas passes through gas exit passage 14 and a small proportion enters the gas space existing above the liquid within the liquid reservoir chamber 11, but the majority exits the gas vaporization zone via gas exit passage 15.

Liquid absorbant material 17 is in communication with the liquid reservoir chamber 11 via liquid transfer material 18. Liquid transfer material 18 is a capillary material and by capillary action supplies liquid to the external surface of liquid absorbant material 17. The liquid then passes through said material 17 to the cavity. As shown the liquid transfer material is the same material as the liquid absorbant material but it need not be.

Liquid reservoir chamber 11 also comprises flow path restricter 19 which restricts the flow of saturated gas into liquid reservoir chamber 11 and together with the base of core 12 forms gas exit passage 14 The flow path restrictor includes a layer of liquid absorbant material.

Spacers 20 are provided between liquid reservoir chamber 11 and gas vaporization zone 10.

Saturated gas passes from gas exit passage 15 through gas outlet control 21 and then mixes with by-pass gas at gas mixing junction 7.

Claims

CLAIMS:

1. A vaporizer comprising gas inlet and outlet ports, gas inlet and outlet control means, at least one liquid reservoir chamber, at least one gas passage, and at least one gas vaporization zone the volume of which remains substantially constant throughout the period of operation of the vaporizer and which comprises one or more gas passages substantially surrounded by liquid absorbant material said material being substantially saturated with liquid from the liquid reservoir chamber, there being liquid communication means between the liquid absorbant material and the liquid reservoir chamber such that liquid is replenished to said liquid absorbant material as vapour passes therefrom to the gas.

2. A vaporizer as claimed in claim 1 wherein the gas vaporization zone is located proximate but is at least partially separate from the liquid reservoir chamber.

3. A vaporizer as claimed in claim 1 or claim 2 wherein gas passing through the gas vaporization zone is substantially saturated before exiting said zone and the greater proportion if not all of the saturated gas does not circulate within the liquid reservoir chamber.

4. A vaporizer as claimed in any preceding claim wherein liquid absorbant material surrounds at least one tubular gas passage within the gas vaporization zone.

5. A vaporizer as claimed in any preceding claim wherein one or more support members are provided proximate one or more layers of liquid absorbant materials and which together with said material form one or more gas passages wherein gas mixes with vapour.

6. A vaporizer as claimed in claim 5 wherein said support member comprises one or more springs, webbing members, hoops, perforated tubes, or a combination thereof.

7. A vaporizer as claimed in any preceding claim wherein the liquid absorbant material is a permeable capillary material.

8. A vaporizer as claimed in claim 7 wherein the liquid communication means comprises at least one layer of liquid absorbant material extending from the liquid in the liquid reservoir chamber to the gas vaporization zone.

9. A vaporizer as claimed in any preceding claim further including a flow path restrictor between the gas vaporization zone and the liquid reservoir chamber so as to restrict the flow of saturated gas which enters the liquid reservoir chamber.

10. A vaporizer as claimed in any preceding claim wherein the gas vaporization zone further comprises a core around which there is at least one spring covered by liquid absorbant material and wherein vapour saturation of the gas occurs in the cavity inside the spring/s and liquid absorbant material.

11. A vaporizer as claimed in claim 1 and substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.