GB2580013A

GB2580013A - Door-closer with overload valve

Info

Publication number: GB2580013A
Application number: GB1815834.5A
Authority: GB
Inventors: Gibbs Simon; Leslie Norcott Stuart; Patrick Mccarthy Bruce
Original assignee: Assa Abloy Ltd
Current assignee: Assa Abloy Ltd
Priority date: 2018-09-28
Filing date: 2018-09-28
Publication date: 2020-07-15
Anticipated expiration: 2038-09-28
Also published as: CN110965883B; GB2580013B; CN110965883A; GB201815834D0

Abstract

A door closer with a first chamber 5 defined by a piston 9 movable between a door open position with a first volume, and a door closed position with a second volume, the first volume being greater than the second volume, with the first and second chambers being connected with a main valve (20 Fig 1) which can hold the door in an open position, and an overload valve 91 such that should pressure within the first chamber exceed a threshold pressure it allows fluid communication between the first and second chambers 5 7. In the door closed position, a protruding head portion 915 on the piston is at least partially received within a corresponding recess 202 located opposite the head portion on the first chamber. The overload valve 91 is located in the protruding head portion of the piston 915. The overload valve may include a spring biased ball bearing 912. The overload valve allows the door to be closed faster than the normal damped motion if the door is pushed. Also claimed is a situation where the piston has a recess and the first chamber has a protruding head portion.

Description

Door-closer with overload valve.

Field of the Invention

The present invention concerns door-closers. More particularly, but not exclusively, this invention concerns a door-closer with an overload valve.

Background of the Invention

A door may be coupled with a door-closer to enable the door to be biased towards a closed position. Prior art door-closers comprise a spring that biases the door-closer into a "door closed" position, and a hydraulic arrangement that ensures controlled movement of the door-closer between a "door open" position and the "door closed" position. In such door-closers, controlled movement is achieved by controlling the rate at which hydraulic fluid moves between chambers situated within the door-closer as the door-closer moves between the "door open" and "door closed" positions.

There may be instances in which it is desirable to forcibly move a door to which a door-closer is coupled from an open to a dosed position at a speed faster than 2 0 that at which the door would close under the control of the door closer alone. If the door closer is forcibly moved from a door open position to a door closed position, the pressure of the hydraulic fluid within the door closer can increase to a level which causes damage to the internal components of the door closer. Known door closers, such as that disclosed in GB2323125A, provide an overload valve, also known as a check valve, which is configured to relieve the hydraulic pressure build-up in such situations. However, even with such overload valves in place it is still possible that the hydraulic pressure within the door closer could reach a level which causes damage when a door to which the door closer is attached is forcibly shut.

The present invention seeks to mitigate the above-mentioned problems. -2 -

Summary of the Invention

The present invention provides a door closer comprising: a first chamber and a second chamber, the first chamber and second chamber in fluid communication via a main valve, the first chamber defined by a piston movable between a door open position, in which the first chamber has a first volume, and a door closed position, in which the first chamber has a second volume, the first volume being greater than the second volume, and an overload valve configured such that should pressure within the first chamber exceed a threshold pressure, the overload valve allows fluid communication between the first chamber and second chamber, wherein the piston has a protruding head portion and the first chamber has a corresponding recess located opposite the protruding head portion, wherein in the door closed position, the protruding head portion is at least partially received within the corresponding recess, the overload valve being located in the protruding head portion of the piston.

The threshold pressure may be greater than 100 Newton-metres. The threshold pressure may bc 120 Newion-metres.

With this configuration, it has been observed that, when the piston is forced from the door open position towards the door closed position, the fluid pressure needed to engage the overload valve can be reached locally at the overload valve inlet 2 0 while the fluid pressure is lower elsewhere within the first chamber. Therefore the overload valve can be engaged, thereby moving fluid from the first chamber into the second chamber via the overload valve, while subjecting the parts of the door-closer elsewhere in the first chamber to a lower pressure than is typical in known door-closers.

2 5 The door closer may comprise a biasing arrangement, for example a spring, arranged to bias the door closer towards the door closed position. The pressure exerted by the biasing arrangement on the first chamber is preferably less than the threshold pressure required to open the overload valve.

The projecting end portion may have a length and the recess may have a depth, the length of the projecting end portion being substantially equal to the depth of the recess. Such an arrangement allows the projecting end portion to be at least partially, and potentially fully, received within the recess. -3 -

When the door closer is in the door closed position, the volume of the first chamber (the second volume) may be at a minimum. When the door closer is in the door closed position, the volume of the second chamber may be at a maximum.

The protruding end portion of the piston may be cylindrical, and the corresponding recess may also be cylindrical. The first chamber, second chamber, and piston may be approximately cylindrical, and the protruding end portion of the piston and corresponding recess may also be cylindrical, with smaller diameters than the first chamber and second chamber. The protruding end portion of the piston may be cuboidal, and the corresponding recess may also be cuboidal. The first chamber, 1 0 second chamber, and piston may be approximately cuboidal, and the protruding end portion of the piston and corresponding recess may also be cuboidal, with smaller dimensions than the first chamber and second chamber.

The protruding end portion may have an end face, and the corresponding recess may have an end face, the end faces being flat, concave, or convex. The shape of the end faces of the protruding end portion and corresponding recess may be arranged to further increase the localised pressure exerted on the overload valve. For example, the end face of the protruding end portion may be convex and the end face of the corresponding recess may be concave, such that the convex end face is approximately the same shape as the concave end face.

2 0 The overload valve may be located in the centre of the end face of the protruding end portion of the piston. Locating the overload valve in the centre of the end face of the protruding end portion of the piston may further increase the localised pressure exerted on the overload valve.

When the piston is in the door open position, the length of the projecting end portion may be more than 10% of the distance between the first and second ends of the first chamber. When the piston is in the door open position, the length of the projecting end portion may be more than 15% of the distance between the first and second ends of the first chamber. The length of the projecting end portion may be more than 5 millimetres.

The main valve may be configured to be able to be shut so that substantially no fluid can move between the first and second chambers via the main valve. Such an arrangement may allow the door closer to hold a door in a door open position. The -4 -door-closer may be an electro-hydraulic door-closer and the main valve may be configured to be able to be shut in response to the presence of an electric field. Such an arrangement may allow for the door holder to hold a door in a door open position by generating an electrical field, and the door closer to allow a door to be closed by removing the electrical field. Such an arrangement may be useful to allow automatic closing of doors during a fire alarm.

According to a second aspect, the invention provides a door closer comprising: a first chamber and a second chamber, the first chamber and second chamber in fluid communication via a main valve, the first chamber defined by a piston movable 1 0 between a door open position, in which the first chamber has a first volume, and a door closed position, in which the first chamber has a second volume, the first volume being greater than the second volume, and an overload valve configured such that should pressure within the first chamber exceed a threshold pressure, the overload valve allows fluid communication between the first chamber and second chamber, wherein the piston has a recessed end portion, and the first chamber has a corresponding protruding hcad portion located oppositc thc recessed end portion, wherein in the door closed position, the protruding head portion is at least partially received within the corresponding recess, the overload valve located in the recessed end portion of the piston.

2 0 According to a third aspect, the invention provides a door comprising a door-closer according to either of the first aspect or second aspect of the invention. According to a fourth aspect, the invention provides a method of closing a door according to the third aspect of the invention, the door beginning in the door open position, and a user applying pressure to the door such that the threshold pressure is exceeded, and fluid is transferred through the overload valve of the door closer, such that the door moves into a door closed position.

It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the door closer of the second aspect of the invention may include any of the features described in relation to the first aspect of the invention.

The skilled person will realised that the second aspect of the invention provides a mirrored piston and recess arrangement as described with regards to the first aspect of -5 -the invention, and the features of the invention described with reference to the first aspect of the invention may be reverse as appropriate when applied to the second aspect of the invention. Additionally, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa.

Description of the Drawings

Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which: Figure 1_ is a schematic drawing of a door to which a door-closer according to an embodiment of the invention is coupled which shows the door in a fully open position; Figure 2 is a cross-sectional view of a door-closer according to an embodiment of the invention which shows the door-closer with the piston in a "door open" position, Figure 3 is a cross-sectional view of the door-closer of Figure 2 which shows the door-closer with the piston in a "door closed" position; Figure 4 is a cross-sectional view of the door-closer of Figure 2 showing the 2 0 showing the different positions the piston moves through when moving from a "door open" to a "door closed" position; Figure 5 is an exploded view of the main valve assembly of the door-closer; Figure 6 is a detailed cross-sectional view of the main valve assembly of the door-closer; Figure 7 is a cross-sectional view of the door-closer of Figure 2 showing the overload valve arrangement in detail; and Figure 8 is a detailed cross-sectional view of the main valve assembly of the door-closer configured so that the door-closer can be topped-up with hydraulic fluid. -6 -

Detailed Description

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

The door-closer 1, which is shown in more detail in Figures 2 and 3, is an electro-hydraulic door-closer and comprises a main body 3 with a hollow cylindrical internal cross-section that is partitioned into a first chamber 5 and a second chamber 7 by a piston 9 that is movable along the main body 3 to change the relative volumes of the first and second chambers 5, 7. The first chamber 5 and second chamber 7 are in fluid communication with one another via a soft-close valve 11 connected 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, and is thereby able to prevent fluid flow between the first and second chambers to allow a door to which the door-closer is coupled to be held 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, opposing wall of the first chamber such that as the piston 9 is driven along the main body 3 towards the main valve assembly 20, the volume of the first chamber reduces and hydraulic fluid is moved from the first chamber 5 into the soft-close valve 11 via main valve assembly 20 and then into the second chamber 7. The door-closer thereby being arranged such that fluid is moveable between the first and second chambers 5, 7 via the main valve assembly 20 and soft close valve 11 at every position of the piston 9, provided that the main valve assembly is open. The door closer further comprises a door-speed valve 16 and a latch-control valve 17 through which fluid can flow between the first chamber 5 and the second chamber 7 depending on the position of the piston 9 within the main body 3, as will be described in more 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 as shown in Figure 1 with an angle A of 130 degrees, and a "door closed" position in which the door is fully closed (corresponding to an angle A of 0 degrees as shown in Figure 1). The door-closer 1 is shown with the piston 9 in the "door open" position in Figure 2 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. The door-closer 1 is shown with the piston 9 in the "door closed" position in Figure 3 wherein the piston 9 is positioned such that the volume of the first chamber 5 is at a minimum arid the volume of the second chamber 7 is at a maximum. The door-closer 1 comprises a spring 15 which is located inside the main body 3 and which abuts the piston 9 to bias the piston 9 into the "door closed" position. Such an arrangement ensures that when the door-closer is coupled to a door, the door will always be biased towards the door closed position.

As the piston 9 is moved by a user from the "door closed' position to the "door open" position, the pinion of a rack and pinion arrangement 13 is rotated by a mechanical linkage (not shown) in a manner known per se, in a clockwise direction as seen in Figures 2 and 3 and drives the piston 9 against the resilient bias of the spring 15, from left to right as shown in Figures 2 and 3, reducing the volume of the second chamber 7 and increasing thc volume of the first chamber 5. As this happens, thc changes in the relative sizes of the first arid second chambers forces hydraulic fluid contained within the second chamber 7 to move to the first chamber 5 via the soft close valve 11 and main valve assembly 20 and, depending on the position of the piston 9, the door-speed valve 16 and latch-control valve 17. Once the door to which the door-closer 1 is coupled is fully open, the main valve assembly 20 can be operated to hold the piston 9 in the "door open" position, as will be described in more detail below.

When the piston is in the "door open' position and the main valve assembly 20 is opened, the door to which the door-closer 1 is coupled is moved by the door closer 1 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, under the control of the door-closer. The speed at which the piston 9 moves varies depending on 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 phases: a soft-close phase which corresponds to the door moving between and angle A of 130 and 75 degrees from the door closed position, a door speed phase which corresponds to the door moving between an angle -8 -A of 75 and 10 degrees from the door closed position, and a latch speed phase which corresponds to the door moving between and angle A of 10 and 0 degrees from the door closed position. The operation of the door-closer 1 as the piston 9 moves from the "door open" position to the "door closed" position through each of these phases will now be described with reference to Figure 4.

As can be seen in Figure 4, the first chamber 5 feeds a speed control valve 16 and a latch control valve 17, each of which are connected to a feedback valve 18 such that fluid can move from the speed control valve 16 and latch control valve 17, into the return valve 18 and into the second chamber. However, with the piston 9 in the "door open" position, as shown in Figure 4, the feedback valve 18 is blocked by the piston 9. As the piston 9 moves towards the opposing wall 240 of the chamber (the opposing wall 240 being formed by the main valve assembly 20), from right to left as shown in Figure 4 between positions A and B, the piston 9 moves through the soft-close phase. In the soft-close phase hydraulic fluid can flow through the main valve 20 and soft-close valve II only, and not through either of the speed control valve 16 or the latch control valve 17 due to the return valve 18 being blocked by the piston 9. In the soft-close phase, therefore, operating the main valve assembly 20 prevents any fluid flow between the first and second chambers 5, 7.

The piston 9 moves through the door speed phase between positions B and C 2 0 as shown in Figure 4. When the piston 9 reaches position B, the piston 9 now no longer blocks the return valve 18, so as the piston 9 moves beyond position B, the piston pushes hydraulic fluid from the first chamber 5 into the second chamber 7 via the speed control valve 16 and latch control valve 17, as well as via the main valve assembly 20 and soft-close valve 11. The speed with which the door closes during the door speed phase is controlled by adjusting the speed control screw 161 which can be moved into or out of the return valve 18 to obstruct the fluid flow through the return valve 18.

The piston 9 moves through the latch speed phase between position C and position D, which corresponds to the "door closed" position, as shown in Figure 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- -9 -close valve 11. The speed with which the door closes during the latching phase can be controlled by adjusting the latch control screw 171 which can be moved into or out of the return valve 18 in the same way as the speed control screw 161.

The main valve assembly 20, an exploded view of which is shown in Figure 5, is positioned at an end of the main body 3, opposite the piston 9, and forms an opposing wall 240 of the first chamber 5. As can be seen in Figures 5 and 6, the main valve assembly 20 comprises 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 chamber 207 of the valve pin housing 203, and a pin piston 209, contained within an interior chamber 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 comprises a first valve port 221 at a first end of the valve pin housing 203 and a second valve port 223 in the wall of the valve pin housing 203. The valve pin housing 203 is arranged such that all hydraulic fluid flowing between the first and second chambers 5, 7 must flow through the interior chamber 207 of the valve pin housing 203 via the valve ports 221 and 223.

The pin 205 is substantially cylindrical in shape and has a first portion 217 of a first diameter and a second portion 219 of a second, larger diameter. The diameter of the second portion 219 is substantially equal to the internal diameter of the interior chamber 207 of the valve pin housing 203 such that movement of the valve pin 205 within the valve pin housing 203 is restricted to a direction along a longitudinal axis of the valve pin housing 203, in a direction as indicated by the arrow labelled "Y" in Figure 6. The valve pin 205 has a first conical end 211 and a second, opposite flat end 213. The first end 211 being the leading end of the pin 205 at the first portion 217 and the second end 213 being the trailing end of the pin at the second portion 219.

The first valve 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 valve port 221. The first valve port 221 is formed by a conical recess which is shaped to receive the first end 211 of the pin 205, such that the pin 205 may be moved from an open position, along the axis of the pin chamber and into a closed position in which the conical first end 211 of the pin 205 sits within the conical recess, as shown in Figure 6. In this position, the valve pin -10 - 205 closes the valve port 221 and prevents fluid flow through the main valve assembly 20.

The valve pin 205 is moved into contact with the valve inlet 221 by a valve piston 209 which is arranged to move under the influence of the magnetic field generated by a 24 V coil 225. This type of electromagnetic piston arrangement will be well understood by the skilled person. 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 moveable along the longitudinal axis of the pin piston 209 such that an adjustable length of the adjustable member 227 projects 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 towards 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 into a position in which 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, thereby bypassing the main valve assembly 20 soft-close valve 11, speed control valve, and latch control valve. The overload valve 91, shown in detail in Figure 7, comprises a valve spring 913 which biases a ball bearing 912 into a position in which the ball bearing 912 blocks a valve inlet 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 forcibly moved from the open position to the closed position, the increase in hydraulic pressure within the first chamber 5 increases to a level which causes the ball bearing 912 to push against the resilient bias of the spring 913 thereby unblocking the valve inlet 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 damaging the door-closer due to an over-pressurisation of the first chambers.

As can be seen in Figure 2 and Figure 3, the piston 9 forms a first end of the cylindrical first chamber 5 and the main valve assembly 20 forms a second, opposite end of the first chambers, the volume of the first chamber 5 thereby being changeable by moving the piston 9 towards or away from the main valve assembly 20. The piston 9 comprises a cylindrical projecting end portion 915 that projects into the first chamber 5, the axis of the cylindrical end portion 915 being aligned with the axis X of the first chamber 5 so that the projecting end portion 915 is located centrally within the first chamber. The overload valve 91 is located within the projecting end portion 915 such that the overload valve inlet 911 is positioned at the centre of the projecting end portion 915, aligned with the axis X of the first chamber 5.

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

Configuring the door-closer 1 with the overload valve inlet 911 positioned on a projecting end portion 915 of the piston 9 and by arranging the second wall of the chamber with a recess 202 configured to receive the projecting end portion 915 of the piston 9 as the piston 9 is moved into the door closed position has been found to be advantageous. With this configuration, it has bccn observed that, whcn the piston 9 is forced from the door open position towards the door closed position, the fluid pressure needed to engage the overload valve 91 can be reached locally at the overload valve inlet 911 while the fluid pressure is lower elsewhere within the first chamber 5. Therefore 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 instances the amount of hydraulic fluid within the door-closer 1 may need topping-up. For this reason the main valve assembly is provided with a vacuum valve 225 at the far end of the pin-piston housing 210, opposite the main body 201 of the main valve assembly 20, as shown in Figure 6. The vacuum valve 225 comprises a screw-threaded bore 227 that is in fluid communication with the pin piston chamber 211 via an aperture 228 located at an end of the bore 227, the screw-threaded bore 227 having a tapered section adjacent the aperture 228 such that aperture 228 has a diameter that is smaller than the diameter of the main section of the bore 277. To seal the vacuum valve 225, a ball bearing 230 having a diameter larger than the diameter of the aperture 228 is first placed into the bore 227 and then a grub screw 229 is -12 -screwed into the bore 227 to push the ball bearing 230 along the bore 227 and into abutment with the sloping internal walls 231 of the tapered section of the bore 227 adjacent the aperture 228. When the vacuum valve 225 is sealed, therefore, the aperture 228 is blocked by the ball bearing 230.

To top-up the door-closer 1 with hydraulic fluid, the latch control valve 17 is removed and a source of hydraulic fluid 173 is placed at the latch control valve inlet 172 so that the source of hydraulic fluid 173 is in fluid communication with the first or second chamber 5, 7, depending on the position of the piston, as shown in Figure 8. The ball bearing 230 and grub screw 229 are then removed from the bore 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 bore 227 using, for example, a syringe or pump connected to the tube 400, to suck any air contained within the door-closer 1 in the direction of the arrow labelled -.Z" in Figure 8. The application of a vacuum at the vacuum valve 225 causes hydraulic fluid to be sucked from the hydraulic fluid source 173, in the direction of the arrow labelled "W" in Figure 8, thereby replacing any trapped air within the door-closer 1 with hydraulic fluid. Once the hydraulic fluid within the door-closer 1 has been topped-up to a suitable level, the ball bearing 230 and grub screw 229 are replaced within the bore 227 to seal the vacuum valve 225.

Where in the foregoing description, integers or elements are mentioned which 2 0 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. It will also be appreciated by the reader 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. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.

Claims

-13 -Claims I. A door closer comprising: a first chamber and a second chamber, the first chamber and second chamber in fluid communication via a main valve, the first chamber defined by a piston movable between a door open position, in which the first chamber has a first volume, and a door closed position, in which the first chamber has a second volume the first volume being greater than the second volume, 1 0 and an overload valve configured such that should pressure within the first chamber exceed a threshold pressure, the overload valve allows fluid communication between the first chamber and second chamber, wherein the piston has a protruding head portion and the first chamber has a corresponding recess located opposite the protruding head portion, wherein in the door closed position, the protruding head portion is at least partially received within the corresponding recess, the overload valve being located in the protruding head portion of the piston.
2 A door closer as claimed in claim 1, wherein the projecting end portion has a length and the recess has a depth, the length of the projecting end portion being substantially equal to the depth of the recess.
3 A door closer as claimed in any preceding claim, wherein the protruding end portion of the piston is cylindrical, and the corresponding recess is also cylindrical.
4 A door closer as claimed in any preceding claim, wherein the protruding end portion has an end face, and the corresponding recess has an end face, the end faces being flat, concave, or convex.
5 A door closer as claimed in claim 4, wherein the overload valve is located in the centre of the end face of the protruding end portion of the piston.
-14 - 6. A door-closer as claimed in any preceding claim, wherein, when the piston is in the door open position, the length of the projecting end portion is more than 10% of the distance between the first and second ends of the first chamber.
7. A door-closer as claimed in any preceding claim, wherein the main valve is configured to be able to be shut so that substantially no fluid can move between the first and second chambers via the main valve.
8. A door-closer as claimed in claim 7, wherein the door-closer is an electro- 1 0 hydraulic door-closer and the main valve is configured to be able to be shut inresponse to the presence of an electric field.
9. A door closer comprising: a first chamber and a second chamber, the first chamber and second chamber in fluid communication via a main valve, thc first chambcr defined by a piston movable between a door opcn position, in which the first chamber has a first volume, and a door closed position, in which the first chamber has a second volume, the first volume being greater than the second volume, 2 0 and an overload valve configured such that should pressure within the first chamber exceed a threshold pressure, the overload valve allows fluid communication between the first chamber and second chamber, wherein the piston has a recessed end portion, and the first chamber has a corresponding protruding head portion located opposite the recessed end 2 5 portion, wherein in the door closed position, the protruding head portion is at least partially received within the corresponding recess, the overload valve being located in the recessed end portion of the piston.
10. A door comprising a door-closer according to any preceding claim
11. A method of closing a door, the door as claimed in claim 10 the door beginning in the door open position, and a user applying pressure to the door such that -15 -the threshold pressure is exceeded, and fluid is transferred through the overload valve of the door closer, such that the door moves into a door closed position.