GB2606553A

GB2606553A - PEEP valve and method of manufacture

Info

Publication number: GB2606553A
Application number: GB2106805.1A
Authority: GB
Inventors: Thomas Wragg Alistair; George Alexander Drew Jamie; Deborah Hemmings Claire
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 2021-05-13
Filing date: 2021-05-13
Publication date: 2022-11-16
Also published as: GB202106805D0

Abstract

A respiratory valve 1, suitable for use in providing positive end respiratory pressure (PEEP) for a user or patient, has a valve body 2 and a valve cap 4 which define an enclosed volume. A flexible diaphragm 3 (e.g., formed from silicone) arranged within the enclosed volume separates it into first and second chambers. At least one inlet conduit 6 to receive respiratory gases and at least one outlet conduit 8 are also provided; wherein the flexible diaphragm is arranged to stretch over the inlet conduit/s in the first chamber such that a biasing force retains the diaphragm in a blocking position. The diaphragm deforms away from the blocking position when sufficient air pressure force overcomes this biasing force, allowing respiratory gases to flow from the inlet conduit/s to the outlet conduit/s, exiting from the valve. A method of manufacture of the said valve is also presented.

Description

PEEP VALVE AND METHOD OF MANUFACTURE Technical Field of the Invention The invention relates to respiratory valves for providing positive end respiratory pressure (PEEP) for a user or patient.

Background to the Invention

Positive end respiratory pressure (PEEP) is a positive pressure that remains in a patient's airways at the end of the respiratory cycle. It is a variable that can be controlled by mechanical ventilators to mitigate the risk of lung collapse at the end of a patient's breath. In mechanical ventilation, PEEP can be applied through the use of respiratory PEEP valves. These valves need to have excellent reliability owing to their medical use with patients often in critical conditions. This necessitates precision manufacturing that can make PEEP valves relatively expensive to produce, despite the requirement in certain applications for PEEP valves to be disposable.

PEEP valves are mechanical devices that typically comprise an inlet to an enclosed volume in a valve body through which respiratory gases can be received from a user, and an outlet from the enclosed volume through which respiratory gases are released into the environment. To achieve a reliable PEEP the valve comprises a blocking member or diaphragm that is biased towards a blocking position in which the flow of gases between the conduits is prevented. The blocking member or diaphragm is configured to be moveable or deformable from the blocking position by an air pressure force generated as a result of a user breathing through the valve. The threshold air pressure force to cause movement or deformation of the blocking member or diaphragm is set by a biasing force. This biasing force may be established as a result of a biasing means such as a spring, by gravity acting on a blocking member, or as a result of the resilience and resistance to deformation of a diaphragm.

The manufacture of prior art PEEP valves often necessitates injection moulding of components owing to complex shapes and designs. Such a manufacturing process can be arduous, necessitating design, manufacture and build of supplementary injection moulding tools, often adding to manufacturing costs. Furthermore, diaphragm based valves often rely on a diaphragm being arranged adjacent an inlet conduit in the blocking position to block the flow of respiratory gases. This can be insufficient for reliable sealing against the inlet conduit, and supplemental biasing means are often required such as spring biasing which further adds to the complexities of manufacture.

Therefore it is an aim of the present invention to provide an alternative PEEP valve that mitigates these issues.

Summary of the Invention

According to a first aspect of the invention there is provided a positive end expiratory pressure (PEEP) valve, comprising a valve body attached to a valve cap to define an enclosed volume, a flexible diaphragm being arranged within the enclosed volume to separate the volume into first and second chambers, an inlet conduit for receiving respiratory gases from a user extending into the first chamber from an exterior side of the valve body, and an outlet conduit through which respiratory gases can exit the valve extending from the first chamber to the exterior side, wherein the flexible diaphragm is further arranged to stretch over the inlet conduit in the first chamber such that a biasing force retains the diaphragm in a blocking position in which respiratory gases are prevented from flowing between the conduits, the flexible diaphragm being configured to deform away from the blocking position when an air pressure force in the inlet conduit acting on the diaphragm overcomes the biasing force, such that respiratory gases are permitted to flow from the inlet conduit to the outlet conduit and therefrom to exit the valve.

According to a second aspect of the invention there is provided a ventilator comprising the PEEP valve of the first aspect of the invention.

According to a third aspect of the invention there is provided a method of manufacturing the PEEP valve of the first aspect of the invention, the method comprising the steps of providing a valve body and a valve cap attachable each other to define an enclosed volume, the valve body comprising an inlet conduit for receiving respiratory gases and an outlet conduit through which respiratory gases can exit the valve, the conduits extending through the valve body from an exterior side to the enclosed volume; arranging a flexible diaphragm within the enclosed volume to separate the volume into first and second chambers, such that the inlet and outlet conduits extend from the exterior side of the valve body to the first chamber; and then attaching together the valve body, flexible diaphragm and the valve cap; wherein the step of arranging the flexible diaphragm within the enclosed volume comprises stretching the diaphragm over the inlet conduit in the first chamber such that a biasing force retains the diaphragm in a blocking position in which respiratory gases are prevented from flowing between the conduits, and such that the flexible diaphragm can deform away from the blocking position into the second chamber when an air pressure force in the inlet conduit acting on the diaphragm overcomes the biasing force, such that respiratory gases are permitted to flow from the inlet conduit to the outlet conduit and therefore to exit the valve.

The PEEP valve comprises discrete components that can be manufactured using computer numerical control (CNC) equipment from bar stock of suitable material. Therefore the PEEP valve can be manufactured without the requirement for supplementary mould design and manufacture. Furthermore the components are arranged so as to operate as a reliable PEEP valve without the requirement for supplementary biasing means, further reducing the complexities of manufacture. This is owing to the use of a diaphragm stretched over the inlet conduit -rather than being merely arranged adjacent to the conduits -to obtain a biasing force that retains and adequately seals the diaphragm in a blocking position.

The valve body and valve cap are discretely separate components that when attached to each other define a volume or cavity between them that is enclosed. The enclosed volume may be of any shape, but preferably is a substantially cylindrical volume. The cap may for instance comprise a top wall and a peripheral wall, the peripheral wall of the cap attaching to a side of the valve body, such that the side of the valve body acts as a lower wall to allow the volume defined by the cap to be completely enclosed. The exterior of the valve body and cap can take any particular form, providing that both can attach to each other as required to define the enclosed volume. The valve body and cap are preferably made from a stock material suitable for CNC manufacture such as polycarbonate. The valve body and cap may be attached together using screws, bolts, adhesive, or other fastening means. Preferably the fastening means comprises a plurality of bolts equi-spaced around the periphery of the cap. This has been shown to provide a uniform seal of the cap to the valve body.

A flexible diaphragm is arranged within the enclosed volume separating the volume into first and second chambers. The flexible diaphragm extends entirely across the enclosed volume such that the first and second chambers are not in fluid connection. The flexible diaphragm may be attached at its periphery to the cap or valve body to maintain such a configuration, or may be sandwiched between the cap and valve body at its periphery. The flexible diaphragm therefore has a cross sectional area that substantially conforms to the cross sectional area of the enclosed volume, and may comprise peripheral apertures through which any fastening means (bolts for instance) used to attach the valve body to the cap can pass. The diaphragm itself is formed from a flexible material such as silicone rubber that can be stretched and deformed in use, whilst also being suitable for cutting to size using CNC equipment.

The valve body also comprises both inlet and outlet conduits that extend from an exterior side into the first chamber. The inlet and outlet conduits preferably extend parallel each other to further aid manufacture using CNC equipment which is well suited to linear drilling. Respiratory gases from a user are intended to be received into the inlet conduit, to flow into the first chamber, and to exit the valve through the outlet conduit. The inlet conduit may therefore be located on the exterior side within an inlet port that protrudes from the valve body for connecting to a respiratory hose from a ventilator or similar. The outlet conduit may vent directly to atmosphere. The inlet and outlet conduits may extend to the first chamber, or partially into the first chamber. The cross sectional shape of the inlet conduit and outlet conduit is preferably circular for simplicity of manufacture.

The flexible diaphragm is arranged to stretch over the inlet conduit. This exerts a tensile force on the flexible diaphragm urging it to seal against the inlet conduit, thereby preventing gas flow. Such a seal is considered reliable with respect to merely arranging the diaphragm adjacent or in abutment with the inlet conduit, as in such circumstances no additional biasing force is established. When respiratory gases flow into the inlet conduit they are therefore blocked from further propagation by the diaphragm. This causes a pressure increase in the inlet conduit. As the pressure increases (for instance by virtue of a user or patient continuing to exhale into the inlet conduit), the resultant air pressure force acting on the diaphragm will match and then exceed the biasing force resulting from the tensile forces acting on the diaphragm. The diaphragm, owing to it's inherent flexibility, will deform into the second chamber of the enclosed volume and therefore away from the blocking position. This allows respiratory gases to flow into the first chamber and out of the outlet conduit. As respiratory gases continue to flow, the air pressure in the inlet conduit reduces until the air pressure force acting on the diaphragm is less than the biasing force. The diaphragm returns under the action of the biasing force to the blocking position, preventing gas flow. This maintains a PEEP in the inlet conduit and therefore with a user of the valve, that is controllable by the magnitude of the biasing force.

In preferred embodiments the inlet conduit protrudes into the first chamber to form an upstand urging against the flexible diaphragm in the blocking position. By providing the inlet conduit as an upstand urging against the diaphragm, the diaphragm is stretched over the upstand causing a biasing force resulting from tensile stresses in the diaphragm itself. The height of the upstand can thus be set to determine the strength of the biasing force and therefore the PEEP the valve is configured to operate at. Preferably the height of the upstand is adjustable such that the PEEP value can be adjusted. The inlet conduit may for instance be a tube attached into the valve body using threaded means. By rotating the inlet conduit relative to the valve body, the upstand height inside the first chamber may be adjusted.

In some embodiments the PEEP valve comprises a plurality of inlet conduits forming the upstand. This enables respiratory gases to flow more readily into the valve. The upstand preferably is arranged concentric to a major axis of the valve body so as to act centrally and uniformly on the diaphragm. Centralised conduits can also be grouped within an inlet port protruding from the exterior of the valve body for connection to a respiratory hose. Preferably there are a plurality of outlet conduits to permit gases to flow more easily out of the valve. Even more preferable is that these are arranged as a ring of outlet conduits concentrically around the upstand. The outlet conduits can thereby be arranged around the base of the upstand to allow for uniform venting of gas from the first chamber to the exterior of the valve.

Preferred embodiments comprise an o-ring arranged between the flexible diaphragm and the valve body. The o-ring provides a seal between the valve body and the flexible diaphragm preventing respiratory gases escaping the first chamber to the exterior of the valve without having navigated the outlet conduit. The o-ring is seated radially outwards from the location of the inlet conduits and outlet conduits.

Some embodiments comprise a valve cap having a gas bias port to the second chamber, such that a pressurised gas can be provided into the second chamber to urge against the flexible diaphragm thereby adjusting the biasing force. Pressurised gas provided into the second chamber causes a pressure increase in the second chamber, urging the flexible diaphragm towards the blocking position. Resultantly the overall biasing force is increased, necessitating a greater air pressure in the inlet conduit to deform the flexible diaphragm away from blocking the inlet conduit. Therefore a greater PEEP is achieved. The pressurised gas in the second chamber may be adjusted to adjust the overall PEEP. The gas bias port may be of any type suitable for connecting a pressurised gas hose or gas cylinder directly.

Preferably the flexible diaphragm is formed of silicone. Silicone rubber can be cut to size using CNC equipment and is sufficiently flexible and deformable for use in the PEEP valve. The flexible diaphragm is preferably sandwiched between the valve body and valve cap around its periphery such that it is held fixed during use.

It is preferable that the valve body and valve cap are attached together at their periphery using a plurality of equi-spaced bolts. This has been shown by the inventor to provide a uniform seal of the valve body to the valve cap. Even more preferable is that nine bolts are used for attaching the valve body to the valve cap.

Brief Description of the Drawings

Embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings, in which: Figure 1 provides an illustration of an embodiment of a PEEP valve in exploded view; Figure 2a provides an illustration of a valve body of an embodiment of a PEEP valve in cross sectional side view; Figure 2b provides an illustration of a valve body of an embodiment of a PEEP valve in plan-view; Figure 3a provides an illustration of a valve cap of an embodiment of a PEEP valve in cross sectional side view; Figure 3b provides an illustration of a valve cap of an embodiment of a PEEP valve in plan-view; and Figure 4 provides an illustration in plan-view of an embodiment of a flexible diaphragm of a PEEP valve. Detailed Description Figure 1 provides an illustration of an embodiment of a PEEP valve 1 in exploded view. The PEEP valve 1 comprises a valve body 2 adjacent a flexible diaphragm 3 and a valve cap 4. The valve body 2 has a substantially frustoconical appearance, the narrower end of the valve body 2 comprises an inlet connector 5 for connecting to the respiratory hose, the wider end of the valve body 2 being adjacent the flexible diaphragm 3. Inlet conduits 6 extend from an exterior surface of the valve body 2 within the inlet connector 5 to an upstand 7 at the wider end of the valve body 2 that protrudes towards the diaphragm 3. There are seven inlet conduits 6 visibly arranged in the central upstand 7. Surrounding the upstand 7 are a plurality of outlet conduits 8 that extend to the exterior of the valve body 2 external to the inlet connector 5. The conduits 6 and 8 are all linear and have a circular cross section. The wider end of the valve body 2 comprises an annular recess 9 concentric to the valve body 2 and located at a radius greater than that which corresponds to the location of the outlet conduits 8. The annular groove seats an o-ring 13 for sealing the valve body 2 to the flexible diaphragm 3. Substantially at the circumference of the wider end of the valve body 2 there are located nine equally spaced holes 10 for receiving bolts 11 from the valve cap 4. This permits the valve body 2 and valve cap 4 to be fastened together. The valve body 2 itself is formed from a single piece of polycarbonate using CNC manufacturing methods.

The flexible diaphragm 3 is shown as a relatively thin layer formed from silicone having the same cross sectional area as the wider end of the valve body 2. Accordingly the diaphragm 3 has nine peripheral holes 3a aligned with the holes 9 of the valve body 2 and through which bolts 11 from the valve cap 4 can pass.

The valve cap 4 is shown as a cylindrical part having a side wall 4a and upper wall 4b. The upper wall 4b is shown with nine equally spaced holes 12 around its circumference. Bolts 11 can pass through these holes 12 for connecting to the valve body 2. A central aperture 14 is also visible and forms a gas bias port through which gas can be provided to urge against the flexible diaphragm 3. The valve cap 4 is also formed from a single piece of polycarbonate. When the valve body 2 and the valve cap 4 are connected by the bolts 11, the flexible diaphragm 3 is sandwiched at its periphery between the cap 4 and valve 2. This causes the diaphragm to also be stretched to cover the inlet conduits 6 on the upstand 7. This provides a biasing force that retains the flexible diaphragm 3 in a blocking position in which respiratory gases are prevented from flowing out of the inlet conduits 6 and into a first chamber defined by the volume between the valve body 2, the flexible diaphragm 3 and the o ring 13. In operation, the flexible diaphragm 3 is able to deform and move away from the blocking position into a second chamber defined between the diaphragm 3 and valve cap 4.

Figure 2a provides an illustration of the valve body 2 of Figure 1 in cross sectional side view. The valve body 2 has a substantially frustoconical cross section with a wide substantially circular end 2a of 60mm diameter for positioning adjacent a flexible diaphragm, and a narrow end 2b of 23mm formed as an inlet port 5 for connecting to a respiratory hose. The inlet port 5 is substantially cylindrical and extends into the valve body 2 a depth of 34mm to form a cavity. The overall length of the valve body 2 is 42mm. At the base of the cavity are a plurality of linear inlet conduits 6 that extend through the valve body 2 to the substantially circular end 2a. The linear inlet conduits 6 each have a diameter of 5mm. Protruding from the substantially circular end 2a of the valve body 2 is an upstand 7. The upstand 7 has a narrower diameter than the valve body 2 and protrudes from the substantially circular end 2a a distance of 1mm. The inlet conduits 6 extend through the upstand 7 to define a route for respiratory gases through the valve body 2. Around the base of the upstand 7 are indicated positions for a plurality of linear outlet conduits 8 arranged equidistantly from each other. The outlet conduits 8 extend from the substantially circular end 2a of the valve body 2 back through the valve 2 to an exterior surface of the valve outside of the inlet port 5. The outlet conduits 8 have a diameter of 4mm and provide a route for respiratory gases back through the valve body 2. Encircling the upstand 7 and outlet conduits 8 at the substantially circular end 2a of the valve body 2 is a recess 9 for seating an o-ring. The recess 9 has a width of 3mm. At the periphery of the substantially circular end 2a of the valve body 2 there is shown a bolt hole 9 extending partially back into the valve body 2. The bolt hole 10 receives a bolt from the valve cap such that the valve body 2 can be secured to the valve cap to create the PEEP valve. Whilst not visible in the cross sectional view, a plurality of these bolt holes 10 are provided in the valve body 2.

Figure 2b provides an illustration of the valve body 2 of Figure 1 in plan-view showing the substantially circular end 2a. The substantially circular end 2a has a circular cross section defining the peripheral edge of the valve body 2. Adjacent the peripheral edge are nine bolt holes 10 arranged in an equidistant manner around the substantially circular end 2a. Radially inwards of the bolt holes 10 is a recess 9 for seating an o-ring. Radially inwards of the recess 9 are twelve outlet conduits 8 arranged in a circular configuration around the base of an upstand 7. The upstand has a circular cross section. Located centrally to the upstand are a cluster of seven inlet conduits 6.

Figure 3a provides an illustration in cross sectional side view of the valve cap 4 shown in Figure 1. The valve cap 4 has a tray like cross section with side walls 4a and upper wall 4b with overall diameter of 60mm and overall depth of 15mm. The valve cap 4 defines a volume 15 that can be enclosed by a flexible diaphragm arranged to extend across and between the side walls 4a. This volume 15 has a rectangular cross section having dimensions of 37.5mm width and 10mm depth. The volume 15 when closed by a diaphragm becomes the second chamber of the PEEP valve. A central aperture 14 is arranged in the upper wall 4b of the valve cap 4 that is in fluid connection with the volume 15. In-use this permits supplementary pressurised gas to be introduced to the volume 15 to permit adjustment of PEEP. A linear hole 12 is also shown extending through the length of the side wall 4a. This hole 12 receives a bolt 11 through the upper wall 4b that extends through the valve cap 4 and into a valve body of a PEEP valve. Nine such holes 12 are arranged around the valve cap 4. In-use a flexible diaphragm arranged across the side walls 4a may deform into the volume 15 forming the second chamber of the PEEP valve.

Figure 3b provides an illustration in plan view of the valve cap 4 shown in Figure 1. The valve cap 4 has a circular cross section of 60mm diameter. Radially inwards of the circumference of the valve cap 4 are nine equally spaced holes 12 for receiving bolts. Radially inwards of the holes 12 is the periphery of the volume 15 defined by the side walls 4a. This is shown as having a circular cross section. Arranged centrally to the volume 15 and on the axis of the valve cap 4 is the central aperture 14 which also has a circular cross section but with a narrower diameter than that of the volume 15.

Figure 4 provides an illustration in plan-view of the flexible diaphragm 3 shown in Figure 1. The flexible diaphragm 3 is formed from silicone rubber and is precision cut to have a circular cross section with 60mm diameter and thickness of 0.5mm. Nine peripheral holes 3a are provided equally spaced adjacent the circumference of the diaphragm 3. The holes 3a have diameters of Smm.

When the PEEP valve 1 is assembled and in-use, respiratory gases from a user are received from inlet port 5 through inlet conduits 6 and into the valve 1. The respiratory gases are trapped within the inlet conduits 6 owing to diaphragm 3 being stretched over upstand 7 and therefore stretched over the openings from the inlet conduits 6. This creates a biasing force sealing the inlet conduits 6 reliably. As respiratory gases continue to be introduced into the inlet conduits 6 a pressure increase occurs that acts on the flexible diaphragm 3. This creates an air pressure force acting on the flexible diaphragm 3 to oppose the biasing force. When the air pressure force exceeds the biasing force the diaphragm 3 is urged away from the inlet conduits 6 into the second chamber volume 15 within the valve cap 4. This deformation of the diaphragm permits respiratory gases to flow from the inlet conduits 6 into the first chamber volume defined between the valve body 2, diaphragm 3, and o-ring 13. This volume is connected to the exterior of the valve 1 through outlet conduits 8. Therefore respiratory gases flow from the inlet conduits 6 to the outlet conduits 8 and to the exterior of the valve. Resultantly the respiratory gas pressure in the inlet conduits 6 reduces and the air pressure force acting on the diaphragm 3 decreases. This causes the air pressure force to drop below the biasing force caused by the tensile forces acting on the diaphragm 3. The diaphragm 3 therefore moves back towards the upstand 6 and being stretched over the inlet conduits 6. The inlet conduits 6 become sealed again preventing respiratory gas flow leading to a positive pressure being retained in the inlet port 5 and therefore with the user of the valve 1. The process is repeated in accordance with the breathing cycle.

Whilst the embodiments are described with reference to particular external profiles and dimensions this is not intended to be limiting. The exact quantity of features such as the inlet and outlet conduits may be varied from the precise numbers described herein according to intended application.

Claims

CLAIMS1. A positive end expiratory pressure (PEEP) valve, comprising a valve body attached to a valve cap to define an enclosed volume, a flexible diaphragm being arranged within the enclosed volume to separate the volume into first and second chambers, an inlet conduit for receiving respiratory gases from a user extending into the first chamber from an exterior side of the valve body, and an outlet conduit through which respiratory gases can exit the valve also extending from the first chamber to the exterior side, wherein the flexible diaphragm is further arranged to stretch over the inlet conduit in the first chamber such that a biasing force retains the diaphragm in a blocking position in which respiratory gases are prevented from flowing between the conduits, the flexible diaphragm being configured to deform away from the blocking position into the second chamber when an air pressure force in the inlet conduit acting on the diaphragm overcomes the biasing force, such that respiratory gases are permitted to flow from the inlet conduit to the outlet conduit and therefrom to exit the valve.
2. The PEEP valve of claim 1, wherein the inlet conduit protrudes into the first chamber to form an upstand urging against the flexible diaphragm in the blocking position.
3. The PEEP valve of claim 2, wherein the height of the upstand is adjustable.
4. The PEEP valve of any one of claims 2-3, comprising a plurality of inlet conduits forming the upstand.
5. The PEEP valve of any one of claims 2-4, wherein the upstand is arranged concentrically to a major axis of the valve body.
6. The PEEP valve of any one of claims 2-5, comprising a plurality of outlet conduits.
7. The PEEP valve of claim 6, wherein the plurality of outlet conduits are arranged as a ring of outlet conduits around the upstand.
8. The PEEP valve of any preceding claim, further comprising an o-ring arranged between the flexible diaphragm and the valve body.
9. The PEEP valve of any preceding claim, where in the valve cap comprises a gas bias port to the second chamber, such that a pressurised gas can be provided into the second chamber to urge against the flexible diaphragm to adjust the biasing force.
10. The PEEP valve of any preceding claim, wherein the flexible diaphragm is formed of silicone.
11. The PEEP valve of any preceding claim, wherein the flexible diaphragm is sandwiched between the valve body and valve cap around its periphery.
12. The PEEP valve of any preceding claim, wherein the valve body and valve cap are attached together at their periphery using a plurality of equi-spaced bolts.
13. The PEEP valve of any preceding claim, wherein the inlet and outlet conduits extend parallel each other between the first chamber and exterior side.
14. A ventilator comprising the PEEP valve of any preceding claim.
15. A method of manufacturing the PEEP valve of claim 1, comprising the steps of: a) Providing a valve body and a valve cap attachable each other to define an enclosed volume, the valve body comprising an inlet conduit for receiving respiratory gases and an outlet conduit through which respiratory gases can exit the valve, the conduits extending through the valve body from an exterior side to the enclosed volume; b) Arranging a flexible diaphragm within the enclosed volume to separate the volume into first and second chambers, such that the inlet and outlet conduits extend from the exterior side of the valve body to the first chamber; and then c) Attaching together the valve body, flexible diaphragm and the valve cap; wherein the step of arranging the flexible diaphragm within the enclosed volume comprises stretching the diaphragm over the inlet conduit in the first chamber such that a biasing force retains the diaphragm in a blocking position in which respiratory gases are prevented from flowing between the conduits, and such that the flexible diaphragm can deform away from the blocking position into the second chamber when an air pressure force in the inlet conduit acting on the diaphragm overcomes the biasing force, such that respiratory gases are permitted to flow from the inlet conduit to the outlet conduit and therefore to exit the valve.
16. The method of claim 15 wherein the step of providing the valve body and valve cap comprises machining the valve body and valve cap from respective bar blocks of material.
17. The method of claim 16 wherein the step of machining the valve body and valve cap further comprises machining the valve body to comprise an upstand for urging against the flexible diaphragm.
18. The method of any one of claims 16-17 wherein the step of machining the valve body and valve cap further comprises drilling the inlet and outlet conduits through the valve body to extend parallel each other.