This invention relates to a door closing device for urging an opened door towards its closed position relative to a doorframe.

More particularly, the invention concerns improvements in a door closer, which is of the kind that usually acts between a door leaf and a doorframe. This type of door closer typically comprises a housing, a plunger movable along the housing, a biasing element disposed in the housing and biasing the plunger inwardly of the housing, and a tension member having one end connected to the plunger and another end, which extends to an anchor element. The housing is normally installed in a bore in the door leaf and the anchor element installed in the doorframe. However, the positions of the housing and the anchor element may be reversed. The biasing element comprises a spring, which operates to bias the plunger, and consequently the tension member, inwardly of the housing, for closing the door. The tension member comprises an articulated element so that the tension member can be bent around the opening angle of the door relative to the door frame.

It is known to provide such concealed door closers with a hydraulic damping assembly, as disclosed for example in GB-A-2441893, GB-A-2441894, WO-A-2005/124079 and WO-A-2008/102115. The hydraulic damping assembly comprises a piston and cylinder assembly that can damp the movement of the plunger. The hydraulic damping assembly comprises circuit for the hydraulic fluid that incorporates an adjustable valve assembly. The valve can be adjusted to vary the damping force of the hydraulic damping assembly.

Recently, a standard classifying controlled door closing devices has been established as BS EN 1154 1997, with Amendment Al 2003. Door closers intended for use on fire resisting doors and smoke control doors are covered by a Construction Products Directive mandate issued by the European Commission, and the Amendment Al to the BS EN 1154 1997 harmonised the standard in compliance with the Directive and allows application of the CE mark. The standard sets minimum performance parameters for door closer operation, in particular with regard to closing moment (dependent on door size and mass) and closing time. While face fixed overhead closers can readily be constructed so as to comply with BS EN 1 154 1997, because a bulky housing can be provided which merely needs to fit to the door face or the frame, in contrast concealed door closers of the type disclosed in EP-A- 0016445 generally cannot, primarily as a result of the inherently low power characteristics of this construction, because the spring needs to be dimensioned to fit within the door leaf without compromising the structural integrity of the door, which is crucial for fire resisting doors, for example.

There is a need in the art for concealed door closers that can comply with BS EN 1154 1997.

We have found that for concealed door closers incorporating a hydraulic damping assembly this demanding performance criterion is difficult to meet because the door closer can suffer from inadvertent jamming, and because it is necessary to ensure that the door closes completely, which means a reliable high closing force right at the end of the closing stroke to overcame any resistance to closing from the latch mechanism for the door.

A door closer having a structure which can meet the British Standard BS.EN 1154, and its equivalent European Standard EN 1 154 is required to pass a simulated lifetime test of 500,000 opening and closing cycles. We have found that sometimes the prior door closers identified above jammed inexplicably during this test, often towards the end of the test, even though the disclosed constructions had particular structural arrangements to prevent jamming of the foam accumulator.

The present invention at least partially aims to overcome the problems of the known door closers described hereinabove. The present invention aims in particular to provide a concealed door closer having a high reliability, with minimum jamming during an extended lifetime.

Accordingly, the present invention provides a door closer comprising: (a) a housing for fitting into a door, the housing having a mounting plate with an opening adjacent to a central bore of the housing;

(b) a tension member extending longitudinally within the central bore of the housing and extending outwardly of the housing through the opening to define an end thereof for fitting to a door frame;

(c) a movable body within the housing and adapted for longitudinal movement within the central bore, the movable body being connected to the tension member;

(d) a spring within the housing and biasing the movable body in a first direction away from the mounting plate so as to urge the tension member inwardly of the housing in a door closing motion;

(e) a hydraulic assembly for hydraulically controlling the longitudinal movement of the movable body, the hydraulic assembly being disposed within the central bore of the housing; wherein the hydraulic assembly comprises a piston coupled to the housing and slidable in a fluid-filled chamber within the movable body, wherein the piston divides the chamber into two compartments, and the piston comprises a valve mechanism which opens to permit relatively free movement of the fluid from one compartment to the other when the movable body is moved relative to the piston in a second direction, opposite to the first direction, in response to movement of the tension member outwardly of the housing but closes to present resistance to movement of the movable body in the first direction,

wherein the fluid-filled chamber comprises an first elongate chamber within which the piston slides and a second elongate chamber in fluid communication therewith via first and second longitudinally separated fluid ports, the first and second chambers and first and second fluid ports defining a hydraulic loop, and

an accumulator comprising a compressible foam body disposed in the fluid-filled chamber at a location adjacent to the hydraulic loop.

The present invention further provides a door closer comprising:

(a) a housing for fitting into a door, the housing having a mounting plate with an opening adjacent to a central bore of the housing;

(b) a tension member extending longitudinally within the central bore of the housing and extending outwardly of the housing through the opening to define an end thereof for fitting to a door frame; (c) a movable body within the housing and adapted for longitudinal movement within the central bore, the movable body being connected to the tension member;

(d) a spring within the housing and biasing the movable body in a first direction away from the mounting plate so as to urge the tension member inwardly of the housing in a door closing motion;

(e) a hydraulic assembly for hydraulically controlling the longitudinal movement of the movable body, the hydraulic assembly being disposed within the central bore of the housing; wherein the hydraulic assembly comprises a piston coupled to the housing and slidable in a fluid-filled chamber within the movable body, wherein the piston divides the chamber into two compartments, and the piston comprises a valve mechanism which opens to permit relatively free movement of the fluid from one compartment to the other when the movable body is moved relative to the piston in a second direction, opposite to the first direction, in response to movement of the tension member outwardly of the housing but closes to present resistance to movement of the movable body in the first direction,

wherein the fluid-filled chamber comprises an first elongate chamber within which the piston slides and a second elongate chamber in fluid communication therewith via first and second longitudinally separated fluid ports, the first and second chambers and first and second fluid ports defining a hydraulic loop, and

an accumulator comprising a compressible foam body held in a fixed translational position within the first elongate chamber and separated from contacting the piston by a separation element.

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

FIG. 1 is a partly cut-away perspective side view of a door closer according to an embodiment of the present invention in a closed configuration;

FIG. 2 is a partly cut-away perspective side view of the door closer of FIG. 1 in an open configuration; FIG. 3 shows an exploded perspective view of the plunger valve assembly of the door closer of FIG. 1 ;

FIG. 4 shows a side view of the plunger valve assembly of the door closer of FIG. 1 in a first, closed, configuration;

FIG. 5 shows a side view of the plunger valve assembly of the door closer of FIG. 1 in a second, open, configuration; and

FIG. 6 shows an enlarged side section of part of the plunger valve assembly of the door closer of FIG. 1.

Figures 1 to 6 show a door closer according to the present invention that can be used for urging an opened door towards its closed position relative to a door frame;

An elongate housing 2 in the form of a cylindrical tube comprises a biasing element 4 in the form of a helical compression spring 4. In Figures 1 and 2, for clarity of illustration only the opposed ends of the helical compression spring 4 are shown and the central portion is not shown. A plunger 6 is disposed in and movable along the housing 2. The plunger 6 is biased inwardly of the housing 2 by the biasing element 4. The helical compression spring 4 annularly surrounds the plunger 6. The housing 2 has a mounting plate 8 affixed thereto, the mounting plate 8 having holes 10 extending therethrough for receiving fixing screws. In use, the housing 2 is received in an elongate horizontal cavity in a door leaf (not shown), and the mounting plate 8 is rebated into the edge of the door leaf and affixed thereto, for example by screws.

A rigid tension member 14 has a first end 16 pivotally connected at a first pivot 18 to a plunger head 17 of the plunger 6 and a second end 20 pivotally connected at a second pivot 22 to an anchor element assembly 24. The first pivot 18 has a knurled outer cylindrical surface 19 securely fitting into a cylindrical hole 21 in the plunger head 17, the knurling preventing inadvertent removal of the first pivot 18. The anchor element assembly 24 comprises a mounting member 26, in the form of a plate, for mounting in a door frame (not shown) and an elongate link member 30 extending from the mounting member 26. The mounting member 26 is typically rebated into the edge of the door frame and affixed thereto, for example by screws. The second pivot 22 is located at a free end 32 of the link member 30 remote from the plate member 26. The first and second pivots 18, 22 have parallel axes 19, 23.

Conceivably, the mounting positions of the housing 2 and the anchor element assembly 24 may be reversed, with the housing 2 received in the door frame and the anchor element assembly 24 mounted to the door leaf.

A hole 34 in the mounting plate 8 permits movement therethrough of the rigid tension member 14 and the link member 30.

The rigid tension member 14 comprises a linearly straight body that has a laterally offset reduced thickness central portion 37 between the first and second ends 16, 20.

The door closer of the invention also incorporates an adjustable damper to provide a decelerated or damped closing action.

In the illustrated embodiment a hydraulic cylinder/piston damper 50 for damping the movement of the plunger 6 within the housing 2, having the general structure as disclosed for example in WO-A-2005/124079, is provided. The hydraulic cylinder/piston damper 50 has a threaded adjuster pin 52 for adjusting the operation of the hydraulic damper 50. The threaded adjuster pin 52 is mounted in the plunger head 17 of the plunger 6 adjacent the first pivot 18 and has an elongate head 54 which extends away from the plunger 6 and lies adjacent to the rigid tension member 14. At the other end of the threaded adjuster pin 52 a needle valve member 55 of a restrictor valve is provided which is employed to adjust the flow of hydraulic fluid in the damper 50. This provides a valved fluid port 81. The hole 34 permits insertion therethrough of a screwdriver or other tool to adjust the threaded adjuster pin 52.

At the other end of the housing 2 a cylindrical end piece 56 is fitted into the housing 2 so as to close off the bore 5 defined by the housing 2. A piston shaft, hereinafter referred to as a plunger shaft 60, is fitted to the end piece 56 and extends axially along a portion of the bore 5, typically about one half of the length of the bore 5. A reduced diameter portion 62 of the plunger shaft 60 extends through a hole 63 in the end piece 56, and a lock nut 64 is threaded onto an end of the plunger shaft 60 on the exposed face of the end piece 56. This arrangement permits the longitudinal position of the plunger shaft 60 in the bore 5 to be adjusted over a small distance after manufacture and assembly of the door closer by turning the lock nut 64.

The closed door position is shown in Figure 1. The mounting plate 8 and the plate member 26 abut. The rigid tension member 14 is wholly received in the housing 2, and the link member 30 is also received in the housing 2. The helical compression spring 4 has urged the plunger 6 to its most inward position with respect to the housing 2.

When the door leaf is opened relative to the door frame about the axis of one or more door hinges (not shown), the plunger 6, being attached to the door frame, is pulled in a direction outwardly of the housing 2. Accordingly, the helical compression spring 4 is progressively compressed, as a result of a compression force acting thereon by the plunger 6, and exerts an inward biasing force acting against the opening pulling force on the door leaf. The open position is shown in Figure 2. The mounting plate 8 is spaced from the plate member 26. The link member 30 is pulled out of the housing 2 and the rigid tension member 14 is partly received in the housing 2. The rigid tension member 14 is rotated relative to the plunger 6 about the first pivot 18. The link member 30 is rotated relative to the rigid tension member 14 about the second pivot 22.

In the fully open position, in which the door leaf has been opened by an angle of up to 120°, the rigid tension member 14 is pulled completely out of the housing 2 and the first pivot 18 and the associated end of the plunger 6 are disposed at the hole 34. The rigid tension member 14 has been rotated relative to the plunger 6 about the first pivot 18 so as to lie, in the fully open position, at an angle of up to about 120° relative to the longitudinal axis of the door closer 2. The link member 30 has been rotated relative to the rigid tension member 14 about the second pivot 22.

After the door leaf is released, the biasing force of the helical compression spring 4 acts to bias the rigid tension member 14 inwardly of the housing 2, for closing the door. The damper may provide a reduced damping force at the end of the closing operation so as to provide an enhanced closing velocity for overcoming any latch resistance so that the door is securely latched when closed.

The structure and operation of the hydraulic damping assembly will now be described.

A hydraulic damper assembly 70 is mounted on the plunger shaft 60 for sliding movement therealong. The hydraulic damper assembly 70 includes an outer tube 72 which extends axially along a portion of the bore 5, typically about one half of the length of the bore 5. The outer tube 72 has an integral radially outwardly directed flange 74 at one end 75 thereof that is towards the end piece 56. The flange 74 and the mounting plate 8 define opposed bearing surfaces against which the opposed ends of a helical compression spring 4 are seated. The helical compression spring 4 surrounds the outer tube 72 and outer tube 72 is free to move along the bore 5 within the internal diameter of the helical compression spring 4 as the spring 4 is progressively compressed or expanded.

At the other end of the outer tube 72 the end edge 71 is crimped radially inwardly to support the plunger head 17 that is fitted within the outer tube 72.

An inner tube 80 is disposed coaxially within the outer tube 32. One end 82 of the inner tube 80 is fitted, in a fluid-tight manner, to the plunger head 17 and another end 84 is fitted to a plunger shaft housing 86 which surrounds the plunger shaft 60. The adjacent end 75 of the outer tube 32 is also fitted to the plunger shaft housing 86.

The inner tube 80, plunger head 17 and the plunger shaft housing 86 define an inner chamber 90 through which the plunger shaft 60 extends. An outer chamber 92 is defined between the outer tube 72 and the inner tube 80. At the plunger head 17 the inner chamber 90 and the outer chamber 92 communicate via the restrictor valve comprising the needle valve member 55. At the plunger shaft housing 86 the inner chamber 90 and the outer chamber 92 communicate via at least one port, described hereinafter, in the inner tube 80. This structure forms a hydraulic circuit connecting the inner and outer chambers 90, 92. The inner chamber 90 and the outer chamber 92 are filled with a hydraulic fluid, such as an oil or ethylene glycol.

The restrictor valve can regulate the flow of hydraulic fluid from the inner chamber 90 to the outer chamber 92, and thereby control the degree of damping of the hydraulic damping assembly.

A piston, referred to hereinafter as a plunger valve assembly 100, is shown in detail in FIGS. 3 to 5.

Referring in particular to FIG. 3, the plunger shaft 60 is provided at its end thereof which is remote from the reduced diameter portion 62 fitted into the end piece 56 with a second reduced diameter portion 102 on which the plunger valve assembly 100 is mounted. The plunger valve assembly 100 comprises, in turn, a plunger boss 104 fitted onto the second reduced diameter portion 102, a plunger washer 105 fitted onto the plunger boss 104, a plunger seal 106 fitted onto the plunger boss 104, a plunger fluid flow plate 1 10 fitted onto the second reduced diameter portion 102, and a lock nut 112, threaded onto the end of the second reduced diameter portion 102 so as to secure the plunger valve assembly 100 on the plunger shaft 60.

The plunger boss 104 and plunger fluid flow plate 110 are prevented against longitudinal movement along the plunger shaft 60 by the lock nut 112. However, as described in detail hereinafter, the plunger washer 105 and the plunger seal 106 are mounted on the plunger boss 104 and have a limited range of longitudinal movement. Movement of the plunger seal 106 causes opening or closing of the plunger valve assembly 100.

The plunger boss 104 has a central hole 113 through which the second reduced diameter portion 102 of the plunger shaft 60 extends. The plunger boss 104 comprises a large diameter end wall 114 whose external diameter, defined by an outer circumferential surface 115 is slightly less than the internal diameter of the inner tube 80. Plural through-holes 11 1 extend through the end wall 114. A channel body 116 of the plunger boss 104, integral with the end wall 1 14, has a reduced diameter as compared to the end wall 1 14. The channel body 116 is substantially cylindrical but includes a plurality, in the embodiment four, longitudinally directed channels 1 18 formed in its outer circumferential surface 120. The channels 1 18 are substantially semi-circular in cross- section and are equidistant around the circumferential surface 120. The channels 1 18 each terminate at a closed end 1 19 located at a position a short distance x (e.g. about 0.5mm) remote from the end face 124 of the end wall 114. The closed end 119 is thus near to but spaced from the annular sealing face 124 of the end wall 114. A junction 121 of the end face 124 and the circumferential surface 120 is spaced from both the closed ends 119 and the through-holes 111, so that when the plunger washer 105 abuts the end face 124, a seal is formed therebetween.

The plunger washer 105 is typically composed of metal and is an annular ring of the same external diameter as the end wall 114 and a thickness greater than the distance x of the closed ends 1 19 from the end face 124. The internal circumferential surface 125 of the plunger seal 106 is slidably fitted on the outer circumferential surface 120 of the channel body 118 of the plunger boss 104 and can move longitudinally thereto. Accordingly, when the plunger washer 105 is slid into a position to the left as shown in FIG. 3 and therefore abuts the end face 124, the washer 105 covers the closed ends 119 of the channels 118 and there is little or no possibility of hydraulic fluid flow from the channels 118 towards the end face 124 because the washer 105 closes off the ends 1 19 of the channels 1 18.

The plunger seal 106 comprises an annular body of plastics or rubber material, and has an external diameter which is substantially the same as the internal diameter of the inner tube 80 so that when the plunger seal 106 is received in the inner tube 70, there is a fluid tight seal between the outer circumferential surface 126 of the plunger seal 106 and the internal surface 128 of the inner tube 80. The internal circumferential surface 130 of the plunger seal 106 is slidably fitted on the outer circumferential surface 120 of the channel body 118 of the plunger boss 104 and can move longitudinally thereto. The annular end face 132 of the plunger seal 106 facing towards the washer 105 constitutes a sealing face which seals against the washer 105 which is turn is urged against the end wall 114 which acts as a seat for the washer 105 which in turn acts as a seat for the plunger seal 106. The plunger fluid flow plate 110 comprises an annular metal disc 148 having a central opening 150 for receiving the second reduced diameter portion 102 of the plunger shaft 20 and a plurality of, in the embodiment six, conduits 152 extending between the opposed annular faces of the disc 148. The conduits 152 are circumferentially equidistant and disposed in a satellite fashion around the central opening 150. The lock nut 1 12 secures the disc 148 to the plunger shaft 60 but leaves the conduits 152 at least partially exposed.

The sealed position of the plunger valve assembly 100 is shown in Figure 4 and the unsealed position is shown in Figure 5.

In the sealed position of FIG. 4, which is achieved when the hydraulic fluid pressure acts in a direction from right to left in the drawing of FIG. 4 during closing of the door closer, in which the assembly of the outer and inner tubes 70, 80 moves to the right in FIG. 1 along the plunger shaft 60, the fluid pressure urges the plunger seal 106 against the washer 105 and the washer 105, in turn, against the end wall 114 of the plunger boss 104. Therefore, when the outer circumferential surface 126 of the plunger seal 106 is sealed against the inner circumferential surface 128 of the inner tube 70, hydraulic fluid within the inner chamber 82 on one side of the plunger seal 106 cannot flow to the other side of the plunger seal 106. By providing the washer 105 together with the closed ends 119 of the channels 1 18 being remote from the end face 124 of the end wall, this minimises the possibility of hydraulic fluid being forced between the plunger seal 106 and the plunger boss 104 in the sealed position, which could otherwise cause inadvertent jamming of the plunger valve assembly 100. A highly efficient seal is provided in this configuration. The closing movement resulting from the spring bias is damped by the restrictor valve.

In FIG. 5 however, which shows the unsealed configuration, the plunger washer 105 and the plunger seal 106 has been urged by hydraulic pressure (in a right hand direction in FIG. 5) away from the end face 124 and towards the plunger fluid flow plate 110. This is achieved during opening of the door closer, in which the assembly of the outer and inner tubes 70, 80 moves to the left in FIG. 1 along the plunger shaft 60. With the outer circumferential surface 126 of the plunger seal 106 still sealed against the internal circumferential surface 128 of the inner tube 80, hydraulic fluid within the inner chamber 92 can flow through the plunger valve assembly 100. Hydraulic fluid can flow through the through-holes 1 11 and even to some extent over the outer circumferential surface 1 15 of the end wall 114, and then radially inwardly through the gap 154 between the end wall 114 and the plunger washer 105, into the now exposed closed ends 119 of the channels 118, longitudinally along the channels 118, radially outwardly under the fluid pressure so as the exit the channels 1 18 between the seal 106 and the fluid flow plate 110, and finally longitudinally through the conduits 152 in the plunger washer 110. There is substantially no seal at the plunger valve assembly 100 in this configuration. The opening movement, against the spring bias, is substantially unrestricted by the plunger valve assembly 100 and is not damped by the restrictor valve.

This seal accordingly has high efficiency, typically from 80 to 90% according to the test of BS EN 1154 1997, or even as high as 92%.

In a modification, the washer 105 may be omitted and the annular plunger seal 106 may be made correspondingly wider in a longitudinal direction so that it directly abuts the sealing end face 124 of the boss 104 in the sealed position.

Turning to Figure 6 which is a schematic diagram, the plunger valve assembly 100, or piston, slides along and within the elongate inner chamber 90. The elongate outer chamber 92 is in fluid communication therewith via the valved fluid port 81 in the plunger shaft housing 86 and via at least one through fluid port 83 extending through the inner tube 80 at a location towards the opposite end of the inner tube 80. The valved fluid port 81 and the at least one through fluid port 83 are therefore longitudinally separated. The inner and outer chambers 90, 92 and valved fluid port 81 and at least one through fluid port 83 define a hydraulic loop 87. The possible fluid flow during use is indicated by double headed arrows.

An accumulator 176 comprises an elongate annular compressible foam member which is disposed in the inner chamber 90 adjacent to the plunger shaft housing 86 and surrounds the plunger shaft 60. The accumulator 176 comprises a body of foamed plastics or rubber material, comprising a closed cell foam structure, such as neoprene. Preferably, the foam has a density of from 0.7 to 0.8 g/cm ³ . Preferably, the foam is a closed cell expanded foam. The accumulator 176 may be circumferentially continuous. Alternatively, the accumulator 176 may have s slit, or a channel, in an outer circumferential surface thereof extending longitudinally along the length of the elongate accumulator 176.

The accumulator 176 is disposed in the fluid-filled inner chamber 90 at a location adjacent to the hydraulic loop 87. In other words, the accumulator 176 is located between the through fluid port 83 and the end of the inner chamber 90 at the plunger shaft housing 86. Accordingly, as hydraulic fluid circulates in the hydraulic loop 87 between the inner and outer chambers 90, 92 via the valved fluid port 81 and the at least one through fluid port 83, there is substantially no fluid flow through the accumulator 176. However, the accumulator 176 is in fluid communication with the hydraulic loop 87.

In the door closers of the preferred embodiments of the present invention, the accumulator 176 expands and contracts under the pressure of the fluid moving between the two sides of the plunger valve assembly l OOwithin the inner tube 80. This enables the door closer to have continuous damping from an opening angle of approximately 90 degrees down to closure of the door.

In contrast, if an accumulator 176 is not provided in accordance with the present invention, the damping action is usually not effective until the door has partially closed from the 90 degree opening position and reached an opening angle about 45 degrees. On initial release of the door from a fully open position, without an accumulator 176 there would be a degree of free-fall, which is inconvenient and even potentially hazardous. The accumulator 176 therefore provides effective damping of the door closing across its range of movement from a fully open position (i.e. 90 degrees of opening) to a fully closed position, ignoring any deliberate absence of damping immediately prior to final closure in the last few degrees of motion to enable the door motion to overcome any latching resistance on final closure. Such absence of damping causes the latching speed to increase to overcome any latch resistance on door closure. Ideally the accumulator 176 should not be compressed by the rear of the plunger valve assembly 100 moving towards the accumulator 176 when the door is opened. In practice, designers of concealed door closers wish to have the smallest length of product to make installation less difficult. In addition, when the door closer is adjusted to reduce or eliminate the latch speed up action, by shifting the location of the piston shaft (e.g. the rear of the piston shaft is screwed outwardly relative to the housing), the plunger valve assembly 100 is brought even closer to the accumulator 176 when the door is opened.

The accumulator 176 is held in a fixed position within the fluid-filled inner chamber 90. In particular, the inner chamber 90 is defined within the cylindrical inner tube 80, and the accumulator 176 is located in a first, end, portion 177 of the cylindrical inner tube 80 which has an enlarged inner radius compared to a second, central, portion 179 of the cylindrical inner tube 80 in which the piston valve assembly 100. The first end portion 177 and second central portion 179 are connected by an internal chamfer 178. During manufacture, the first portion 177 is reamed out to a larger internal diameter as compared to the second central portion 179 of the cylindrical inner tube 80.

A washer 181 having at least one fluid-flow hole 185 therethrough is located between the accumulator 176 and the second portion 179 of the cylindrical inner tube 80. The washer 181 is captive within the first end portion 177 by the internal chamfer 178. Typically, the washer 181 has an outer diameter substantially corresponding to an inner diameter of the first portion 177 of the cylindrical inner tube, and smaller than that of the second central portion 179 so as to be retained for sliding motion within the first portion 177 of the cylindrical inner tube 80. Typically, a plurality of fluid-flow holes 185 is provided. The washer 181 may have a structure similar to that of the plunger fluid flow plate 110.

When a fluid pressure difference builds up in the inner tube 80, this can be accommodated by fluid passing through the fluid-flow holes 185 is and the fluid pressure compressing the accumulator 176. When the excess pressure is released, fluid can flow in the opposite direction. The accumulator 176 and the washer 181 are captive in the enlarged diameter portion 177 of the inner tube 80, with the washer 181 ensuring that the accumulator 176 is kept physically separate from the moving piston valve assembly 100. The accumulator 176 therefore cannot interfere with the free movement of the piston valve assembly 100. The accumulator 176 is also outside the hydraulic loop or circuit 87, and so cannot directly inhibit or prevent free movement of fluid around that circuit. Consequently, inadvertent jamming of the door closer by the accumulator 176 is prevented.

The present invention provides a concealed door closer that can comply with BS EN 1 154 1997, and in particular can pass a simulated opening/closing test of 500,000 cycles. The overall dimensions are compact, so that the door closer can be fitted within the door leaf without compromising the structural integrity of the door. However, the compression spring dimensions, and therefore spring force available for closing the door leaf, are sufficient to comply with BS EN 1 154 1997. The damping assembly is not only compact, being disposed within the internal diameter of the compression spring, but also it is readily adjustable so that the closure period of the concealed door closer can be reliably controlled to be within the limits required by BS EN 1 154 1997. Moreover, the damping characteristics of the concealed door closer can be adjusted after installation, in particular by a person other than a trained installer or engineer, without removal of the unit from the door leaf.