GB2102538A

GB2102538A - Fluid flow control valves

Info

Publication number: GB2102538A
Application number: GB08116196A
Authority: GB
Inventors: Donald Alexander Larner
Original assignee: Fluid Devices Ltd
Current assignee: Fluid Devices Ltd
Priority date: 1981-05-28
Filing date: 1981-05-28
Publication date: 1983-02-02
Also published as: GB2102538B

Abstract

A pressure compensated flow control valve comprises a valve body 2 defining an inlet 7 and an outlet 11, and a closure member 1 slidably positioned within the body 2. Orifices 9 in the member 1 define part of the main flow path between the inlet 7 and the outlet 11. A rise in inlet pressure moves the member 1 against the action of a spring 3 to restrict flow from the inlet to the orifices 9. Further movement of the member 1 to increase this restriction connects the inlet 7 with the outlet 11 via passage means 16, 17 in the closure member 1. The inlet end of the valve body is adapted to project into the interior of hydraulic system component, e.g. the outlet of a pump. <IMAGE>

Description

SPECIFICATION Fluid flow control valves This invention relates to fluid flow control valves.

Such valves are known for limiting fluid flow to a pre-set maximum value which is independent of the fluid pressure applied to the valve and of the back pressure induced by the load resistance on the fluid system containing such valves.

Such valves are known as pressure compensated flow controls or flow limiters. They comprise essentially a control orifice connected in series with a hydrostatically balanced throttling valve, the control connections of which detect the pressure drop induced by flow through the said control orifice; when this flow induced pressure drop rises to a pre-determined value the throttling valve partially closes and thus acts to limit the pressure drop to the pre-determined value thus limiting the flow through the control orifice to a substantially constant value regardless of variations in upstream and downstream pressure.

It is an object of the invention to provide an improved fluid flow control which is exceptionally compact and simple, is relatively cheap to manufacture and which takes up little installation space relative to its flow and pressure capacity.

It is a further object to provide such a valve in which the pre-set flow value can be altered simply by the interchange of a single component.

According to the invention there is provided a fluid flow control valve including a member slidable in a bore of a valve body against the action of resilient means, comprising a first fluid flow path extending from an inlet in the body through a flow control orifice in the member to an outlet in the body means for applying the pressure differential induced across said orifice to opposite end faces of the member so than an increase in fluid flow along said first path increases in net force thereby applied to the member in the sense to move the member against the action of the resilient means the membercoacting with ports formed in the valve body to restrict fluid flow through the inlet and thus through the control orifice, and comprising a second fluid flow path through the member by-passing said control orifice and said flow restricting means and communicating between said inlet and said outlet after the member has caused an initial pre-determined restriction of the flow through said first fluid flow path.

The above and other aspects of the present invention will now be described by way of example with reference to the accompanying drawing the single Figure of which shows a longitudinal axial section through a fluid control valve mounted in another system component.

Referring to the drawing the valve comprises a hydrostatically balanced control spool 1 slidable in the bore of a valve body 2 against the bias action of a compression spring 3 contained in an extension of the valve body and supported therein by a spring rest 4 which is screwed into and retained by the threads of a fluid exit port.

The valve body is normally screwed into the outlet port of a main system component such as a hydraulic pump and the dotted outline in the drawing shows the assembled relationship of the valve body to such an outlet port. The leftward projection of the valve body therefore uses its penetration of the outlet port to effect a necessary and economical change of direction of the fluid flow, which exits from the outlet port via the annular passage 6 and the radial ports 7 into the annular waist of the control spool 8 whence it passes through the control orifice(s) 9 to the interior of the bias spring and thence through the bore 10 in the spring retainer to the exit port 11 and to the rest of the fluid system.

The pressure immediately upstream of the control orifice(s) 9 is ducted via damping orifice 12 to the chamber 13 and thus acts over the full crosssectional area of spool 1 so as to tend to urge it to the right; pressure immediately downstream of the control orifice(s) simultaneously acts over the same full cross-sectional area of the spool at the face 14 and tends to urge same to the left. Increasing flow through the valve as a whole therefore increases the force differential applied to the spool, this eventually rising to the point where the bias load imposed by spring 3 is balanced, whereafter the spool moves progressively to the right to obscure radial ports 7 and thereby throttle the flow entering the valve. In this manner a substantially constant pressure drop is maintained across the control orifice(s).

However, the entry of pressure fluid through radial ports 7 induces additional forces on the spool 1 due to so-called Bernouilli or jet effects the magnitude of which are functions of the pressure drop across the throttle and which tend to urge the spool to the right; with increasing pressure drop across the valve as a whole, therefore, controlled flow tends to diminish progressively from the ideal. An additional feature is therefore added to the mechanism of the valve to compensate for this potential aberration in performance, and takes the form of a separate flow passage comprising the annular groove 15 formed on the exterior of the spool 1, communicating via compensating jet 16 and axial bore 17 to a position immediately downstream of the control orifice(s) 9.

When the spool moves to the right to commence its throttling action, annulus 15 opens directly to radial ports 7 and flow takes place through the fixed jet 16 to by-pass the main regulated fluid stream and unite with it downstream of the main flow regulating machanism; thus the total flow emerging via port 11 is the resultant of two separate components, and judicious choice of sizes for orifice(s) 9 and jet 16 can result in a total flow which is very nearly constant for all conditions of pressure drop across the valve as a whole.

1. A fluid flow control valve including a member slidable in a bore of a valve body against the action of resilient means, comprising a first fluid flow path extending from a inlet in the body through a flow control orifice in the member to an outlet in the body means for applying the pressure differential induced across said orifice to opposite end faces of the

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Fluid flow control valves This invention relates to fluid flow control valves. Such valves are known for limiting fluid flow to a pre-set maximum value which is independent of the fluid pressure applied to the valve and of the back pressure induced by the load resistance on the fluid system containing such valves. Such valves are known as pressure compensated flow controls or flow limiters. They comprise essentially a control orifice connected in series with a hydrostatically balanced throttling valve, the control connections of which detect the pressure drop induced by flow through the said control orifice; when this flow induced pressure drop rises to a pre-determined value the throttling valve partially closes and thus acts to limit the pressure drop to the pre-determined value thus limiting the flow through the control orifice to a substantially constant value regardless of variations in upstream and downstream pressure. It is an object of the invention to provide an improved fluid flow control which is exceptionally compact and simple, is relatively cheap to manufacture and which takes up little installation space relative to its flow and pressure capacity. It is a further object to provide such a valve in which the pre-set flow value can be altered simply by the interchange of a single component. According to the invention there is provided a fluid flow control valve including a member slidable in a bore of a valve body against the action of resilient means, comprising a first fluid flow path extending from an inlet in the body through a flow control orifice in the member to an outlet in the body means for applying the pressure differential induced across said orifice to opposite end faces of the member so than an increase in fluid flow along said first path increases in net force thereby applied to the member in the sense to move the member against the action of the resilient means the membercoacting with ports formed in the valve body to restrict fluid flow through the inlet and thus through the control orifice, and comprising a second fluid flow path through the member by-passing said control orifice and said flow restricting means and communicating between said inlet and said outlet after the member has caused an initial pre-determined restriction of the flow through said first fluid flow path. The above and other aspects of the present invention will now be described by way of example with reference to the accompanying drawing the single Figure of which shows a longitudinal axial section through a fluid control valve mounted in another system component. Referring to the drawing the valve comprises a hydrostatically balanced control spool 1 slidable in the bore of a valve body 2 against the bias action of a compression spring 3 contained in an extension of the valve body and supported therein by a spring rest 4 which is screwed into and retained by the threads of a fluid exit port. The valve body is normally screwed into the outlet port of a main system component such as a hydraulic pump and the dotted outline in the drawing shows the assembled relationship of the valve body to such an outlet port. The leftward projection of the valve body therefore uses its penetration of the outlet port to effect a necessary and economical change of direction of the fluid flow, which exits from the outlet port via the annular passage 6 and the radial ports 7 into the annular waist of the control spool 8 whence it passes through the control orifice(s) 9 to the interior of the bias spring and thence through the bore 10 in the spring retainer to the exit port 11 and to the rest of the fluid system. The pressure immediately upstream of the control orifice(s) 9 is ducted via damping orifice 12 to the chamber 13 and thus acts over the full crosssectional area of spool 1 so as to tend to urge it to the right; pressure immediately downstream of the control orifice(s) simultaneously acts over the same full cross-sectional area of the spool at the face 14 and tends to urge same to the left. Increasing flow through the valve as a whole therefore increases the force differential applied to the spool, this eventually rising to the point where the bias load imposed by spring 3 is balanced, whereafter the spool moves progressively to the right to obscure radial ports 7 and thereby throttle the flow entering the valve. In this manner a substantially constant pressure drop is maintained across the control orifice(s). However, the entry of pressure fluid through radial ports 7 induces additional forces on the spool 1 due to so-called Bernouilli or jet effects the magnitude of which are functions of the pressure drop across the throttle and which tend to urge the spool to the right; with increasing pressure drop across the valve as a whole, therefore, controlled flow tends to diminish progressively from the ideal. An additional feature is therefore added to the mechanism of the valve to compensate for this potential aberration in performance, and takes the form of a separate flow passage comprising the annular groove 15 formed on the exterior of the spool 1, communicating via compensating jet 16 and axial bore 17 to a position immediately downstream of the control orifice(s) 9. When the spool moves to the right to commence its throttling action, annulus 15 opens directly to radial ports 7 and flow takes place through the fixed jet 16 to by-pass the main regulated fluid stream and unite with it downstream of the main flow regulating machanism; thus the total flow emerging via port 11 is the resultant of two separate components, and judicious choice of sizes for orifice(s) 9 and jet 16 can result in a total flow which is very nearly constant for all conditions of pressure drop across the valve as a whole. CLAIMS

1. A fluid flow control valve including a member slidable in a bore of a valve body against the action of resilient means, comprising a first fluid flow path extending from a inlet in the body through a flow control orifice in the member to an outlet in the body means for applying the pressure differential induced across said orifice to opposite end faces of the member so that an increase in fluid flow along said first path increases the net force thereby applied to the member in the sense to move the member against the action of the resilient means the member coacting with ports formed in the valve body to restrict fluid flow through the inlet and thus through the control orifice, and comprising a second fluid flow path through the member by-passing said control orifice and said flow restricting means and communicating between said inlet and said outlet afterthe member has caused an initial predetermined restriction of the flow through said first fluid flow path.

2. A fluid flow control valve as defined in Claim 1 in which fluid enters initially through radial ports disposed around a section of the valve body which projects in an axial sense into the interior of an outlet port of a functionally separate fluid system component.

3. A fluid flow control valve substantially as herein described with reference to the single figure of the accompanying drawing.