VALVE ASSEMBLY

TECHNICAL FIELD

The invention relates to a valve assembly to regulate a flow of fluid by adjusting the distance between a valve seat and a valve body, especially used in high-pressure spray guns,

BACKGROUND ART

Such valve assemblies are known from the literature and comprise a valve housing having a valve seat and a valve body adapted to fit together in a closing relationship when in a closed position, and being positioned in the flow path of a fluid, which is being sprayed while the distance between said valve seat and said valve body is gradually increased

One of the known valve assemblies is illustrated in e g EP 0 228 363, wherein the valve is part of a complete spray nozzle assembly, and it comprises a fixed solid valve body and a moveable tubular valve seat having a radial ring-shaped protrusion on the outer surface thereof, which protrusion is retained in a closing position against the valve body due to the axial force of a compression spring acting on the protrusion.

Releasing the closing position by gradually increasing the distance of the valve seat from the valve body allows an increasing flow of spray fluid to pass through the valve.

Said release is provided by forcing a hydraulic fluid into a circumferential chamber on one side of the radial protrusion opposite the compression spring

The opening force required should be stronger than the combined force from the compression spring and the pressurized spray fluid acting on the cross sectional area of the tubular valve seat.

This means that the hydraulic fluid should provide a rather demanding force in order to initiate opening the valve, whereafter the hydraulic force needs to be decreased very fast or else the valve will immediately open fully. This means that an on-off valve has been provided rather than a linear regulation valve.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a valve assembly that regulates a flow in a linear manner and with less force

According to the invention, this object has been solved by an embodiment of a valve assembly comprising a valve housing, a vaive seat and a valve body adapted to fit in closing relationship into said valve seat in a closed position; said housing having an inlet and an outlet for a pressurized fluid, positioned upstream and downstream of the valve seat, respectively; said closed position being maintained by a closing force, e.g. from a compression spring; and having an open position, wherein the valve seat and/or the valve body are forced away from the other one by an activating mechanism. This solution is characterized by a pressure balancing line for the moveable valve member, wherein fluid of the fluid flow downstream of the valve seat is in fluid connection with the opposite end of said member, when in operation.

In an advantageous embodiment of the invention, the activating mechanism is a hydraulic fluid forced into an annular chamber defined between the inner wall of the valve housing and the outer surface of a tubular valve seat, whereof an integral radially protruding flange is forced axially in one direction by the spring and in the opposite direction by the hydraulic fluid in order for the valve seat to close or open the gap between the valve seat and the valve body, respectively.

The activating mechanism could also be a hydraulic fluid forced into an annular chamber defined between the inner wall of the valve housing and the outer surface of a valve body, whereof an integral radially protruding flange is forced axially in one direction by the spring and in the opposite direction by the hydraulic fluid in order for the valve seat to close or open the gap between the valve body and the valve seat.

Furthermore, in an embodiment of the invention wherein the balancing line provides fluid connection between the outlet area downstream of the valve seat and a balancing cavity upstream of the valve seat, said cavity surrounds the upstream end of the moveable valve seat, thereby balancing the two ends of the moveable valve seat.

In yet another advantageous embodiment of the invention, the sectional area of the end of the tubular valve seat proximate to the valve member equals the sectional area of the balancing cavity or chamber defined between an outer periphery of the tubular valve seat and the valve housing distal from the valve member.

BRIEF DESCRIPTION OF THE DRAWINGS

After having defined how the invention fulfills the object and provides a valve assembly which is easy and precise to regulate from being fully closed to fully open, a detailed description of a preferred embodiment will be presented, reference being made to the accompanying drawing, in which

Fig 1 is an axial cross section of a valve assemby according to the invention, being in its closed position, and

Fig. 2 is an axial cross section of a valve assemby according to the invention, being in its open position.

DETAILED DESCRIPTION

Fig. 1 and Fig. 2 show a valve assembly 1 being adapted for use in a spray gun structure (not shown), wherein the valve assembly 1 comprises a valve housing 2 having a moveable valve seat 3 and a fixed valve body 4 adapted to fit in closing relationship in said moveable valve seat 3. The valve housing 2 has an inlet 5 and an outlet 6 for a pressurized fluid, said inlet and outlet, respectively, being positioned upstream and downstream of the valve seat.

The closed position is maintained by a closing force of a compression spring 7. An open position, wherein the valve seat is forced away from the valve body, is provided by means of an activating mechanism comprising a hydraulic fluid which is forced into an annular activation cavity 8 defined radially between the outer surface of the axially moveable vaive seat 3 and the inner surface of the valve housing 2 and axially between an inner stop in the housing and a shoulder on the valve seat member, thereby moving the valve seat 3 axially away from the valve body 4 and allowing a fluid flow to pass through the tubular valve seat 3 and around the valve body 4 to the outlet 6,

The moveable valve member 3 is provided with a circumferential protrusion 9 acting as a stop shoulder for one end of the compression spring 7, while the other end thereof is retained by one or more pre-stressing bars 10. The opposite face of the protrusion 9 is stopped against an inner shoulder on the vaive housing 2, avoiding that the valve member 3 and the compression spring 7 leave the valve housing 2.

A balancing line 1 1 establishes fluid connection between an area in the outlet 6 and a balancing cavity 12 provided near the end of the moveable valve seat member and defined radially between the outer surface thereof and the inner surface of the valve housing 2, and axially between an upstream stop in the valve housing 2 and a shoulder on the valve member 3.

In operation, a pressurized spray fluid is attached to the inlet 5 of the valve assembly 1 and is retained in the inlet pipe and the moveable valve seat member 3, which in itself is retained in its closed position by the spring force 7

When the spray gun is to be activated, a hydraulic fluid is forced into the activation cavity 8, thereby displacing the valve seat axially away from the valve body allowing the pressurized spray fluid to pass through the gap between the valve seat 3 and the valve body 4 and into the outlet area 6. When the fluid is in the outlet 6, the pressure of the fluid flow will act on the valve seat member 3, but at the same time the pressure will be balanced by the pressure at the other end of the balancing line, so that the moveable valve seat 3 is in a balanced state and the hydraulic fluid is required only to counteract the spring force 7.

As long as the annular sectional areas of the vaive seat and the balancing cavity, respectively, are equal, a balanced state of the vaive seat member could be retained,

The present embodiment has been described with the valve seat 3 being the moveable member and the vaive body 4 being the fixed member. However, there is no reason why in another embodiment the roles are opposite.

Still the main advantage obtained is a balancing line providing for pressure compensation for the moveable valve member securing a manner to regulate the fluid flow in a linear way from open to closed positions with a moderate effort.

Any type of standard nose cone could be attached to the outlet end 6 of the valve assembly in order to keep good control of the spraying pattern.

Also other means than hydraulic fluid of activating the valve, e.g. mechanical means, could be conceived.