CN110965886A

CN110965886A - Adjustable door closer

Info

Publication number: CN110965886A
Application number: CN201910940320.8A
Authority: CN
Inventors: S·吉布斯; S·L·诺科特; B·P·麦卡锡
Original assignee: Assa Abloy AB
Current assignee: Assa Abloy AB
Priority date: 2018-09-28
Filing date: 2019-09-30
Publication date: 2020-04-07
Anticipated expiration: 2039-09-30
Also published as: GB201815833D0; GB2577541A; GB2577541B; CN110965886B

Abstract

The invention relates to a door closer comprising a first chamber in fluid communication with a second chamber via a first valve, wherein the door closer comprises a piston defining a wall of the first chamber, the piston being movable against the wall on the opposite side of the first chamber to vary the volume of the first chamber, the piston being movable between: -a door open position corresponding to a first chamber having a maximum volume; and-a door closed position corresponding to the first chamber having a minimum volume, wherein the piston is biased towards the door closed position by a resilient biasing member, and wherein the first valve is configured such that fluid can flow between the first and second chambers between the door open and door closed positions across the entire range of motion of the piston, and wherein a flow rate of the fluid through the first valve is adjustable.

Description

Adjustable door closer

Technical Field

The present invention relates to a door closer. More particularly, but not exclusively, the invention relates to a door closer configured such that the speed at which the door closer can close the door is adjustable.

Background

The door may be coupled with a door closer to enable the door to be biased toward a closed position. Prior art door closers include a spring biasing the door closer to a "door closed" position, and a hydraulic arrangement that ensures controlled movement of the door closer between the "door open" and "door closed" positions. In such door closers, controlled movement is achieved by controlling the rate at which hydraulic fluid is moved between chambers located within the door closer as the door closer is moved between "door open" and "door closed" positions.

In some cases, it is desirable that the door be closed at a variable rate when the door is being closed by the door closer. For example, it may be desirable for the door to close at a given speed over most of its range of movement, and then accelerate or decelerate during other stages of closing. For example, at the end of the closing phase, the door may slow down so that it can lock properly without slamming. The speed at which a door closer closes a door depends on the size and weight of the door, and thus a given door closer may not be suitable for use with a wide variety of doors.

The present invention seeks to alleviate the above problems.

Disclosure of Invention

According to a first aspect, the present invention provides a door closer comprising a first chamber in fluid communication with a second chamber via a first valve, wherein the door closer comprises a piston defining a wall of the first chamber, the piston being movable against the wall of the opposite side of the first chamber to vary the volume of the first chamber, the piston being movable between: a door open position corresponding to a first chamber having a maximum volume; and a door closed position corresponding to the first chamber having a minimum volume, wherein the piston is biased toward the door closed position by a resilient biasing member, and wherein the first valve is configured such that fluid can flow between the first and second chambers between the door open and door closed positions across the entire range of motion of the piston, and wherein the fluid flow rate through the first valve is adjustable.

The resilient biasing member may be a spring. The volume of the first chamber may be greater than zero when the piston is in the closed position.

When a door coupled to the door closer is closed, the resilient biasing member moves the piston toward the opposing wall of the chamber, thereby forcing hydraulic fluid from the first chamber into the second chamber via the first valve. Thus, the speed at which the door closes is dependent on the fluid flow rate from the first chamber to the second chamber. However, the closing speed of the door may also be determined by the size and weight of the door to which the door closer is coupled, as the resilient biasing member must push to overcome the force of the door and move fluid from the first chamber to the second chamber. Therefore, a door closer that fixes the flow rate between the first and second chambers would not be suitable for use with a variety of different doors. By providing an adjustable fluid flow rate through the first valve, the door closer of the present invention can be adjusted to accommodate the size and weight of various doors.

The door closer may further include second and third valves configured to enable fluid to move between the first and second chambers via the second and third valves. The piston is movable between a door open position and a first position to move fluid between the first chamber and the second chamber via the first valve and substantially not via the second valve or the third valve. The piston may be movable between a second position and a third position to move fluid between the first chamber and the second chamber via the first valve, the second valve, and the third valve. The piston is movable between a fourth position and a door closed position to move fluid between the first and second chambers via the first and second valves and substantially not via the third valve.

The first location may be adjacent to the second location. The third location may be adjacent to the fourth location. The first position and the second position may be substantially the same position. The third position and the fourth position may be substantially the same position.

Between the second position and the third position of the piston, no fluid may be moved between the first chamber and the second chamber via the third valve. Between the fourth position of the piston and the door closed position, no fluid may be moved between the first chamber and the second chamber via the third valve.

When a door is coupled to a door closer such that the door is movable from a door open position to a door closed position under the control of the door closer, it may be desirable that the speed of door closing differs at different stages of the door closing process. For example, it may be desirable to have a door that can be quickly closed rather than slammed.

Known door closers control the fluid flow rate from the first chamber to the second chamber by using valves through which fluid can flow from the first chamber to the second chamber depending on the position of the piston. For example, it may be desirable to have a "gate speed" stage in which the gate closes at a first speed as fluid moves between the first and second chambers through the first, second, and third valves. When the door approaches the doorframe, it may be desirable to reduce the closing speed for the "door latch" stage, for which reason the valves may be arranged so that during this stage fluid is only allowed to flow through the second and third valves, and substantially not through the first valve.

When a door coupled to the door closer is closed, the door is in a "soft close" phase before reaching a "door speed" phase, wherein the speed of the door closing is controlled solely by the fluid flow rate through the first valve. The speed at which the door closes at this stage will depend on the size and type of door. During this phase, different applications may require the door to close at different speeds, and therefore, embodiments of the present invention may provide a door closer in which the fluid flow rate through the first valve is adjustable, such that the speed at which the door closes during the soft-close phase may be adjusted.

The first valve may comprise a conduit connecting the first chamber and the second chamber, wherein the fluid flow rate may be adjusted by varying the cross-sectional area of the conduit. The first valve may include a flow restricting member that may be moved into or out of the conduit to vary the cross sectional area of the conduit. The flow restricting member may change the cross-sectional area of the conduit by obstructing fluid flow through the conduit. The flow restriction member may alter the cross-sectional area of the conduit by at least partially occluding the conduit. The flow restricting member may be moved to a position to completely occlude the conduit. The flow restricting member may be movable to a position out of the conduit. The conduit may include an axis, and the flow restricting member may move into or out of the conduit at an angle substantially perpendicular to the axis. The flow restriction member may be threaded into or out of the conduit to vary the cross-sectional area of the conduit. The flow restriction member may be a control screw.

The fourth position may correspond to the position the piston is in when the door closer is coupled to the door when the door is positioned between 5 degrees and 15 degrees from the fully closed position of the door. The fourth position may correspond to the position the piston is in when the door closer is coupled to the door when the door is positioned at approximately 10 degrees from the fully closed position of the door.

The first position may correspond to a position of the piston when the door closer is coupled to the door when the door is positioned between 70 degrees and 80 degrees from a fully closed position of the door. The first position may correspond to a position of the piston when the door closer is coupled to the door when the door is positioned at approximately 75 degrees from a fully closed position of the door.

The door closer may include a main valve assembly operable to prevent fluid flow between the first chamber and the second chamber. In an arrangement including a main valve assembly operable to prevent fluid flow between the first and second chambers, the main valve is operable to hold the piston in a door open position. The main valve is operable to maintain the piston in a door closed position. The door closer may be an electro-hydraulic door closer, and the main valve assembly may operate in response to an electric field.

The main valve assembly may be in series with the first valve. The second valve may be in parallel with the first valve. The third valve may be in parallel with the first valve. The second valve may be in parallel with the third valve. A second valve may be in parallel with the main valve assembly. A third valve may be in parallel with the main valve assembly.

According to a second aspect, the present invention provides a door comprising a door closer according to the first aspect of the invention.

According to a third aspect, the present invention provides a method of adjusting a door closer according to the first aspect of the invention, the door closer being arranged such that the first valve further comprises a conduit connecting the first and second chambers and a flow restricting member movable into and out of the conduit to vary the cross-sectional area of the conduit. The method includes the step of moving a flow-restricting member into or out of the conduit to vary the cross-sectional area of the conduit.

It will of course be appreciated that features described in relation to one aspect of the invention may be incorporated into other aspects of the invention. Additionally, the method of the present invention may incorporate any of the features described with reference to the apparatus of the present invention, and vice versa.

Drawings

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which:

FIG. 1 is a schematic view of a door to which a door closer according to an embodiment of the invention is coupled, the schematic view showing the door in a fully open position;

figure 2 is a cross-sectional view of a door closer according to one embodiment of the invention showing the door closer with the piston in the "door open" position;

FIG. 3 is a cross-sectional view of the door closer of FIG. 2 showing the door closer with the piston in the "door closed" position;

FIG. 4 is a cross-sectional view of the door closer of FIG. 2 showing different positions through which the piston moves as it moves from the "door open" position to the "door closed" position;

FIG. 5 is an exploded view of the main valve assembly of the door closer;

FIG. 6 is a detailed cross-sectional view of the main valve assembly of the door closer;

fig. 7 is a cross-sectional view of the door closer of fig. 2 showing in detail the arrangement of the overload valve; and is

Fig. 8 is a detailed cross-sectional view of the main valve assembly of the door closer configured such that the door closer can be replenished with hydraulic fluid.

Detailed Description

Fig. 1 shows a door 100 coupled to a door closer 1 and mounted within a door frame 101 according to an embodiment of the invention. The door 100 is shown in its fully open position in fig. 1, wherein the door is positioned at an angle a of 130 degrees from the door fully closed position (corresponding to the door fully closed position where angle a is 0 degrees, indicated by reference numeral 100' in fig. 1).

The door closer 1, shown in more detail in fig. 2 and 3, is an electro-hydraulic door closer and comprises a main body 3 having a hollow cylindrical internal cross-section, which is divided into a first chamber 5 and a second chamber 7 by a piston 9 which is movable along the main body 3 to vary the relative volumes of the first chamber 5 and the second chamber 7. The first and

second chambers

5, 7 are in fluid communication with each other via a soft shut-off valve 11 coupled in series with a main valve assembly 20. The main valve assembly 20 is operable to prevent fluid flow through the main valve assembly 20, thereby preventing fluid flow between the first and second chambers to allow a door coupled with the door closer to be maintained in an open or closed position.

The piston 9 defines a first wall of the first chamber and the main valve assembly 20 defines a second opposite wall of the first chamber such that when the piston 9 is driven along the body 3 towards the main valve assembly 20, the volume of the first chamber is reduced and hydraulic fluid moves from the first chamber 5 to the soft shut-off valve 11 via the main valve assembly 20 and then into the second chamber 7. Thus, the door closer is arranged such that fluid can move between the first and

second chambers

5, 7 via the main valve assembly 20 and the soft shut-off valve 11 in each position of the piston 9, provided that the main valve assembly 20 is open. The door closer also includes a gate speed valve 16 and a latch control valve 17 through which fluid can flow between the first and

second chambers

5, 7 depending on the position of the piston 9 within the body 3, as will be described in detail below.

When the door closer 1 is coupled to a door, the piston 9 is movable between a "door open" position, in which the door is fully open at an angle a of 130 degrees as shown in fig. 1, and a "door closed"; in the "door closed" position, the door is fully closed (corresponding to angle a of 0 degrees in fig. 1). In fig. 2 the door closer 1 is shown with the piston 9 in the "door open" position, wherein the piston 9 is positioned such that the volume of the first chamber 5 is at a maximum and the volume of the second chamber 7 is at a minimum. In fig. 3 the door closer 1 is shown with the piston 9 in a "door closed" position, wherein the piston 9 is positioned such that the volume of the first chamber 5 is minimal and the volume of the second chamber 7 is maximal. The door closer 1 comprises a spring 15 which is internal to the body 3 and which abuts the piston 9 to bias the piston 9 to a "door closed" position. Such an arrangement ensures that when the door closer is coupled to the door, the door will always be biased towards the door closed position.

When the user moves the piston 9 from the "door closed" position to the "door open" position, the pinion of the rack and pinion arrangement 13 is rotated by a mechanical linkage (not shown) in a self-evident manner, in a clockwise direction as viewed in figures 2 and 3, and drives the piston 9 from left to right as viewed in figures 2 and 3 against the resilient bias of the spring 15, thereby reducing the volume of the second chamber 7 and increasing the volume of the first chamber 5. When this occurs, the change in the relative sizes of the first and second chambers forces the hydraulic fluid contained within the second chamber 7 to move to the first chamber 5 via the soft shut-off valve 11 and the main valve assembly 20 and (depending on the position of the piston 9) the gate speed valve 16 and the latch control valve 17. Once the door to which the door closer 1 is coupled is fully open, the main valve assembly 20 may be operated to hold the piston 9 in the "door open" position, as will be described in detail below.

When the piston is in the "door open" position and the main valve assembly 20 is open, under the control of the door closer, the door closer 1 moves the door to which the door closer 1 is coupled from a fully open position corresponding to an angle a of 130 degrees to a fully closed position corresponding to an angle a of 0 degrees. The speed at which the piston 9 moves varies according to the angle a of the door from the fully closed position. The piston 9 is pushed by the resilient bias of the spring 15 through four stages: a soft closing phase corresponding to the door moving between an angle a of 130 degrees to 75 degrees from a door closed position; a door speed phase corresponding to the door moving between an angle a of 75 degrees to 10 degrees from a door closed position; and a latching speed phase corresponding to the door moving between an angle a of 10 degrees to 0 degrees from the door closed position. The operation of the door closer 1 when the piston 9 moves from the "door open" position to the "door closed" position through each of these stages will now be described with reference to fig. 4.

As can be seen from fig. 4, the first chamber 5 feeds a speed control valve 16 and a latch control valve 17 (each of which is linked to a feedback valve 18) so that fluid can move from the speed control valve 16 and the latch control valve 17 into a return valve 18 and a second chamber. However, as shown in fig. 4, with the piston 9 in the "door open" position, the feedback valve 18 is blocked by the piston 9. When the piston 9 moves towards the opposite wall 240 of the chamber (the opposite wall 240 is formed by the main valve assembly 20), as shown in fig. 4, between position a and position B, the piston 9 moves from right to left through the soft-close phase. In the soft-close phase, since the return valve 18 is blocked by the piston 9, the hydraulic fluid can only flow through the main valve 20 and the soft-close valve 11, and cannot flow through either the speed control valve 16 or the latch control valve 17. Thus, during the soft-close phase, operating the main valve assembly 20 prevents any fluid flow between the first and

second chambers

5, 7.

As shown in fig. 4, the piston 9 moves through the gate speed phase between position B and position C. When the piston 9 reaches position B, the piston 9 now no longer blocks the return valve 18, so when the piston 9 moves beyond position B, the piston pushes hydraulic fluid from the first chamber 5 via the speed control valve 16 and the latch control valve 17 and via the main valve assembly 20 and the soft shut-off valve 11 into the second chamber 7. The rate at which the door closes during the door speed phase is controlled by adjusting a speed control screw 161 that may move into or out of reflux valve 18 to block fluid flow through reflux valve 18.

The piston 9 moves through the latching speed phase between position C and position D (which corresponds to the "door closed" position), as shown in fig. 4. When the piston 9 reaches position C, the piston 9 blocks the speed control valve 16 so that hydraulic fluid can only move between the first chamber 5 and the second chamber 7 via the latch control valve 17, the main valve assembly 20 and the soft close valve 11 valve. The closing speed of the door during the latching phase may be controlled by adjusting a latch control screw 171 that may be moved into or out of the backflow valve 18 in the same manner as the speed control screw 161.

The main valve assembly 20 (an exploded view of which is shown in figure 5) is positioned at the end of the body 3 opposite the piston 9 and forms an opposite wall 240 of the first chamber 5. As seen in fig. 5 and 6, the main valve assembly 20 includes a main valve body 201, a valve pin housing 203 that houses a valve member 205 in the form of a valve pin 205 within an interior cavity 207 of the valve pin housing 203, and a pin piston 209 contained within an interior cavity 211 of a pin piston housing 210. The pin piston 209 is arranged to move the valve pin 205 within the valve pin housing 203. The valve pin housing 203 includes a first valve port 221 at a first end of the valve pin housing 203 and a second valve port 223 in a wall of the valve pin housing 203. The valve pin housing 203 is arranged such that all hydraulic fluid flowing between the first chamber 5 and the second chamber 7 must flow through the inner cavity 207 of the valve pin housing 203 via the valve port 221 and the valve port 223.

The pin 205 is generally cylindrical in shape and has a first portion 217 of a first diameter and a second portion 219 of a larger second diameter. The diameter of the second portion 219 is substantially equal to the inner diameter of the interior cavity 207 of the valve pin housing 203 such that movement of the valve pin 205 within the valve pin housing 203 is limited in a direction along the longitudinal axis of the valve pin housing 203, as indicated by the arrow labeled "Y" in fig. 6. The valve pin 205 has a first tapered end 211 and an opposite second flat end 213. The first end 211 is the leading end of the pin 205 at the first portion 217 and the second end 213 is the trailing end of the pin at the second portion 219.

The first port 221 is aligned with the longitudinal axis of the valve pin housing 203 and the valve pin 205 is positioned within the pin chamber such that the conical first end 211 of the pin faces the first port 221. The first valve port 221 is formed by a tapered recess shaped to receive the first end 211 of the pin 205 such that the pin 205 may move along the axis of the pin chamber from an open position to a closed position where the tapered first end 211 of the pin 205 is located within the tapered recess, as shown in FIG. 6. In this position, valve pin 205 closes valve port 221 and prevents fluid flow through main valve assembly 20.

The valve pin 205 is moved into contact with the valve port 221 by a valve piston 209 arranged to move under the influence of a magnetic field generated by a 24V coil 225. This type of electromagnetic piston arrangement will be well understood by those skilled in the art. However, the pin piston 209 of the present embodiment of the invention further comprises an adjustable member 227 in the form of a grub screw which is movable along the longitudinal axis of the pin piston 209 such that the adjustable length of the adjustable member 227 protrudes from the end of the pin piston 209 in order to adjust the overall length of the piston. Upon application of the electromagnetic field, the piston moves toward the pin and the distal end of the adjustable member 227 abuts the flat end of the pin 205. The pin piston 209 then moves the pin 205 to a position where the first end 211 of the pin 205 is received within the inlet, thereby preventing fluid flow through the main valve.

The door closer also comprises an overload valve 91 which allows hydraulic fluid to flow directly from the first chamber 5 into the second chamber 7 via the overload valve 91, bypassing the main valve assembly 20, the soft shut valve 11, the speed control valve, and the latch control valve. The overload valve 91, which is shown in detail in fig. 7, comprises a valve spring 913 which biases a ball abutment 912 into a position in which the ball abutment 912 blocks the valve orifice 911 so that, in normal use, no fluid can flow between the first and

second chambers

5, 7 via the overload valve 91. If the piston 9 is forced from the open position to the closed position, the hydraulic pressure in the first chamber 5 increases to a level which causes the ball abutment 912 to push against the resilient bias of the spring 913, thereby opening said valve port 911 so that hydraulic fluid can flow from the first chamber 5 into the second chamber 7 via the overload valve. The described overload valve is known and mitigates the risk of damage to the door closer due to over-pressurisation of the first chamber 5.

As can be seen in fig. 2 and 3, the piston 9 forms a first end of the first chamber 5 which is cylindrical and the main valve assembly 20 forms a second end of the opposite side of the first chamber 5, so that the volume of the first chamber 5 is variable by moving the piston 9 towards or away from the main valve assembly 20. The piston 9 comprises a cylindrical protruding end 915 protruding into the first chamber 5, the axis of the cylindrical end 915 being aligned with the axis X of the first chamber 5, so that the protruding end 915 is in the middle inside the first chamber. The overload valve 91 is positioned within the raised end 915 such that the overload valve port 911 is positioned in the center of the raised end 915, aligned with the axis X of the first chamber 5.

At a second end of the first chamber 5, the main valve assembly 20 includes a cylindrical recess 202 having substantially the same dimensions as the protruding end 915, such that the recess 202 is dimensioned to receive the cylindrical protruding end 915 when the piston 9 is moved to the door closed position.

It has been found that it is advantageous to configure the door closer 1 to position the overload valve port 911 on the protruding end 915 of the piston 9, and by arranging the second wall of the chamber as a recess 202 configured to receive the protruding end 915 of the piston 9 when the piston 9 is moved to the door closed position. With this configuration, it has been observed that the fluid pressure required to engage the overload valve 91 can be reached locally at the overload valve port 911, while the fluid pressure is lower elsewhere in the first chamber 5, when the piston 9 is pushed from the door-open position towards the door-closed position. Thus, the overload valve 91 can be engaged while subjecting the first chamber 5 and main valve assembly 20 to a lower hydraulic pressure than is typical in known door closers.

In some cases, the amount of hydraulic fluid within the door closer 1 may need to be replenished. Thus, the main valve assembly is provided with a vacuum valve 225 at the distal end of the pin piston housing 210, on the opposite side of the main body 201 of the main valve assembly 20, as shown in FIG. 6. The vacuum valve 225 includes a threaded bore 227 in fluid communication with the pin piston cavity 211 via an aperture 228 positioned at an end of the bore 227, the threaded bore 227 having a tapered section adjacent the aperture 228 such that the diameter of the aperture 228 is less than the diameter of the main section of the bore 277. To seal the vacuum valve 225, a ball abutment 230 having a diameter greater than the diameter of the aperture 228 is first placed into the bore 227, and a grub screw 229 is then screwed into the bore 227 to push the ball abutment 230 along the bore 227 and into abutment with the inclined inner wall 231 of the tapered section of the bore 227 adjacent the aperture 228. Thus, when the vacuum valve 225 is sealed, the ball abutment 230 blocks the orifice 228.

To replenish the door closer 1 with hydraulic fluid, the latch control valve 17 is removed and a hydraulic fluid source 173 is placed at the latch control valve port 172 such that the hydraulic fluid source 173 is in fluid communication with the first chamber 5 or the second chamber 7 depending on the position of the piston, as shown in fig. 8. The ball abutment 230 and flat head screw 229 are then removed from the hole ₂₂7 and a tube 400 is placed around the end of the pin piston housing 210 as shown in figure 8. A vacuum is then applied to the aperture 227 using, for example, a syringe or pump connected to the tube 400 to draw all air contained within the door closer 1 in the direction of the arrow labelled "Z" in figure 8. Application of vacuum at vacuum valve 225 causes hydraulic fluid to be drawn from hydraulic fluid source 173 in the direction of the arrow labeled "W" in FIG. 8, thereby applying vacuum to hydraulic fluid sourceThe hydraulic fluid replaces all trapped air within the door closer 1. Once the hydraulic fluid in the door closer 1 is replenished to the appropriate level, the ball abutment 230 and grub screw 229 are placed back in the aperture 227 to seal the vacuum valve 225.

In the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. The reader will also appreciate that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Further, it should be understood that such optional integers or features, while potentially beneficial in some embodiments of the invention, may not be desirable in other embodiments and thus may not be present.

Claims

1. A door closer comprising a first chamber in fluid communication with a second chamber via a first valve, wherein the door closer comprises a piston defining a wall of the first chamber, the piston being movable against the wall on the opposite side of the first chamber to vary the volume of the first chamber, the piston being movable between:

-a door open position corresponding to a first chamber having a maximum volume; and

-a door closed position corresponding to a first chamber having a minimum volume,

wherein the piston is biased towards the door closed position by a resilient biasing member, and

wherein the first valve is configured to enable fluid flow between the first chamber and the second chamber across the entire range of motion of the piston between the door open position and the door closed position, and wherein a rate of fluid flow through the first valve is adjustable.

2. The door closer of claim 1, further comprising second and third valves configured such that the fluid is movable between the first and second chambers via the second and third valves, and wherein the piston is movable between:

-the door open position and the first position to move fluid between the first chamber and the second chamber via the first valve and substantially not via the second valve or the third valve;

-a second position and a third position to move fluid between the first chamber and the second chamber via the first valve, the second valve and the third valve;

-a fourth position and the door closed position to move fluid between the first and second chambers via the first and second valves and substantially not via the third valve.

3. The door closer of claim 2 wherein the fourth position corresponds to the position the piston is in when the door is positioned between 5 and 15 degrees from the fully closed position of the door when the door is coupled to the door.

4. A door closer according to claim 2 or 3, wherein the first position corresponds to the position the piston is in when the door is coupled to a door when the door is positioned between 70 and 80 degrees from a fully closed position of the door.

5. A door closer according to any preceding claim, wherein the first valve comprises a conduit connecting the first and second chambers, and wherein the fluid flow rate is adjustable by varying the cross-sectional area of the conduit.

6. A door closer according to claim 5, wherein the first valve comprises a flow restricting member which is movable into or out of the conduit to vary the cross-sectional area of the conduit.

7. The door closer of claim 6 wherein the flow restricting member is a control screw.

8. A door closer according to any preceding claim, wherein the door closer comprises a main valve assembly operable to prevent fluid flow between the first and second chambers.

9. The door closer of claim 8 wherein the door closer is an electro-hydraulic door closer and the main valve assembly is operable in response to an electric field.

10. A door closer according to claim 8 or 9, wherein the main valve assembly is in series with the first valve.

11. A door comprising a door closer according to any preceding claim.

12. A method of adjusting a door closer according to claim 6 or any one of claims 7 to 10 when dependent on claim 6, the method comprising the steps of: moving the flow-restricting member into or out of the conduit to change the cross-sectional area of the conduit.