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

[002] 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.

[003] It is known to provide such concealed door closers with a hydraulic damping assembly, as disclosed for example in WO-A-2005/124079, WO-A-2008/102115 and WO-A-2011/051317. 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.

[004] These known door closers incorporate a specific valve structure which requires highly accurate machining and requires detailed inspection prior to being approved for shipping to customers. For example, WO-A-2011/051317 discloses a plunger head which is formed as a one-piece machined metal body having a pair of external O-ring seals fitted thereto. A threaded adjuster pin comprises an elongate head and a needle valve element. The plunger head has an elongate internal bore for receiving the threaded adjuster pin and has multiple internal diameters for ensuring that the needle valve element accurately controls the rate of flow of hydraulic fluid though the valve. The elongate internal bore is difficult to machine accurately through the plunger head. Furthermore, although not shown in the drawings of WO-A-2011/051317, O-ring seals are provided on the threaded adjuster pin so that the hydraulic fluid does not leak out of the hydraulic damping assembly through the elongate internal bore of the plunger head. Furthermore, when the hydraulic damping assembly is assembled, the O-ring seals on the threaded adjuster pin are required to be inserted into the elongate internal bore, and past multiple internal diameters, including over an internally threaded portion of the elongate internal bore. This structure can increase the difficulty of correct and accurate insertion of the threaded adjuster pin without inadvertent damage to the seals on the threaded adjuster pin.

[005] The present invention at least partially aims to overcome the problems of the known door closers described hereinabove.

[006] The present invention aims in particular to provide a concealed door closer which is easy and cost-effective to manufacture and assemble.

[007] Accordingly, the present invention provides a door closer comprising:

(a) a housing for fitting into a door or to a door frame, 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 or into a door;

(c) a movable body within the housing and configured 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 inward 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 movable body is movable relative to the piston, to cause the fluid-filled chamber to move relative to the piston, in the first inward direction in response to movement of the tension member inwardly of the housing and in a second outward direction, opposite to the first inward direction, in response to movement of the tension member outwardly of the housing in a door opening motion, wherein the fluid- filled chamber comprises a first elongate chamber within which the piston slides and a second elongate chamber in fluid communication therewith via an adjuster for adjusting a damping action of the hydraulic assembly in a door closing motion, the adjuster being located at one end of the fluid-filled chamber, and via at least one fluid return port, located at an opposite end of the fluid-filled chamber, wherein the adjuster of the hydraulic assembly comprises

(i) a head part of the movable body which is connected to the tension member, the head part comprising a first member and a second member which are assembled together, wherein an elongate adjuster bore extends through the first member and the second member and has a first open end located at an outer surface of the head part and a second open end which opens into the first elongate chamber, wherein first and second portions of the elongate adjuster bore are provided in the first and second members respectively, wherein the first portion of the elongate adjuster bore comprises an internally threaded portion and the second portion of the elongate adjuster bore comprises a restrictor valve region, defining an annular internal valve surface, in fluid communication with the first elongate chamber, and wherein the second member further comprises a transverse port fluidically connecting the restrictor valve region and the second elongate chamber;

(ii) an annular lip seal member, having an inner sealing surface, which is disposed in an annular recess within the head part; and

(iii) a rotatable elongate valve member received within the elongate adjuster bore, wherein the rotatable elongate valve member comprises an externally threaded portion which threadably engages the internally threaded portion of the elongate adjuster bore, a sealable portion which extends through, and is sealingly engaged by, the inner sealing surface of the annular lip seal member, and a needle valve element which extends along the restrictor valve region, wherein rotation of the rotatable valve member is configured to adjust a maximum rate of fluid flow between the first and second elongate chambers though the transverse port and the restrictor valve region.

[008] In some preferred embodiments of the present invention, the inner sealing surface of the annular lip seal member is circular and the sealable portion has a cylindrical external surface which is engaged by the inner sealing surface.

[009] In some preferred embodiments of the present invention, the annular lip seal member is composed of an elastomeric material. [010] In some preferred embodiments of the present invention, apart from the annular lip seal member, no other seal or seal member is provided between the rotatable elongate valve member and the elongate adjuster bore.

[Oi l] In some preferred embodiments of the present invention, in the rotatable elongate valve member the externally threaded portion is adjacent to one end of the sealable portion and an opposite end of the sealable portion is adjacent to the needle valve element.

[012] In some preferred embodiments of the present invention, the annular recess containing the annular lip seal member is provided the first member and the first portion of the elongate adjuster bore extends through the annular recess. Optionally, the annular recess is adjacent to an inward end of the internally threaded portion.

[013] In some preferred embodiments of the present invention, the first and second members of the head part have respective opposite first and second transverse surfaces which are assembled together. Optionally, the second member comprises a raised part of the second member which extends above the second transverse surface, and the first member has a cavity extending below the first transverse surface, wherein the raised part is received within the cavity, and the first portion of the elongate adjuster bore extends through the cavity. Further optionally, the annular lip seal member is disposed between the raised part and an inner end of the cavity. Yet further optionally, the raised part has a cylindrical outer surface and the cavity has a cylindrical inner surface.

[014] In some preferred embodiments of the present invention, the annular internal valve surface is cylindrical and the needle valve element has an external frustoconical surface which faces, and is spaced from, the annular internal valve surface. Optionally, wherein an external diameter of the external frustoconical surface decreases in the first inward direction.

[015] In some preferred embodiments of the present invention, the first and second members are assembled together by a threaded element. Optionally, the threaded element has a head portion disposed at a rear face of the second member and a threaded end portion threadably fitted within a threaded bore of the first member. Typically, the threaded element has a longitudinal axis which is transversely offset from a longitudinal axis of the rotatable elongate valve member. More typically, the longitudinal axis of the threaded element and the longitudinal axis of the rotatable elongate valve member are each transversely offset from a central longitudinal axis of the adjuster. [016] In some preferred embodiments of the present invention, the second elongate chamber is annular and surrounds the first elongate chamber which is cylindrical. Optionally, the second elongate chamber is located between an outer tube and an inner tube, and the first elongate chamber is located within the inner tube, an outer surface of the first member is sealed to an inner surface of the outer tube by a first sealing element and an outer surface of the second member is sealed to an inner surface of the inner tube by a second sealing element. Further optionally, the first and second sealing elements comprise O-ring seals.

[017] In some preferred embodiments of the present invention, the piston comprises a valve mechanism which opens to permit relatively free movement of the fluid from one compartment to the other compartment when the movable body is moved relative to the piston in the second outward direction, opposite to the first inward 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 inward direction.

[018] The present invention is predicated on the finding by the present inventor that by providing the plunger head in two separate pieces which are assembled together, the elongate internal bore for receiving the threaded adjuster pin is much easier to machine accurately as compared to the one-piece plunger head disclosed in the Applicant’s earlier WO-A-2011/051317. By providing two separate pieces, each piece can be machined independently, which means that in each piece the respective portion of the internal bore for receiving the threaded adjuster pin has fewer internal diameters than in the entire plunger head. Also, the region of the internal bore which crucially surrounds the needle valve element, which is machined in one of the two pieces, can be very accurately positioned and readily quality-control checked during manufacture. This ensures that the restriction valve accurately controls the rate of flow of hydraulic fluid though the valve in a high quality yet cost-effective product. In summary, as compared to the known one-piece plunger head, by providing the plunger head in two separate pieces which are assembled together, the plunger head is easier to manufacture accurately, inspect and test before assembly.

[019] Furthermore, by providing an annular lip seal which surrounds a sealable portion of the threaded adjuster pin, an effective seal can be provided which exhibits reduced risk of inadvertent damage during assembly, and reduced risk of failure during use of the door closer over the design life of the door closer. Moreover, the single annular lip seal can easily be inserted into a cavity before the two pieces of the plunger head are assembled, so that after assembly the annular lip seal is securely held in a precise position within the body of the assembled plunger head. This structure can provide a highly accurate and durable seal throughout the lifetime of the door closer. Nevertheless, the structure also reduces manufacturing costs, and possible quality control failures, as compared to alternative seals provided on the threaded adjuster pin which is inserted into a one-piece plunger head. As mentioned above, WO-A-2011/051317 discloses a plunger head which is formed as a one-piece machined metal body having a pair of external O-ring seals fitted to the threaded adjuster pin; however, the provision of the annular lip seal, which is disposed in an annular recess within the head part, provided in the door closer of the present invention achieves an improved quality seal and a reduced risk of failure in assembly and performance as compared to the known use of two longitudinally spaced static O-ring seals fitted to the threaded adjuster pin.

[020] 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 a longitudinal cross-section through the plunger head of the plunger valve assembly of the door closer of FIG. 1;

FIG. 4 shows, prior to assembly, the first and second members of the plunger head, and a rotatable elongate valve member for fitting in the plunger head, of the plunger valve assembly of the door closer of FIG. 1; and

FIGs. 5(a) to 5(d) show, respectively, a side view, a top view, a longitudinal cross-section including an enlarged view, and a pair of end views, of the first and second members of the plunger head, prior to assembly, of the plunger valve assembly of the door closer of FIG. 1.

[021] Figures 1 to 5 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.

[022] 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.

[023] 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.

[024] 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.

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

[026] 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.

[027] The door closer of the invention also incorporates an adjustable hydraulic damper assembly 70 to provide a decelerated or damped closing action.

[028] 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.

[029] 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.

[030] 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.

[031] 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 assembly 70 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.

[032] Referring in particular also to FIGs. 3 to 5, which show an opposite left-right orientation of the plunger head 17 compared to FIGs. 1 and 2, and FIG. 3 has parts which are highly schematic, the hydraulic damper assembly 70 for damping the movement of the plunger 6 is provided within the housing 2. The plunger 6, in the form of a movable body, is mounted on the plunger shaft 60 for sliding movement therealong. The hydraulic damper assembly 70 hydraulically controls the longitudinal movement of the plunger 6, and is disposed within a central bore 5 of the housing 2. The hydraulic damper assembly 70 includes an outer tube 72 which extends axially along a portion of the central 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.

[033] 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.

[034] An inner tube 80 is disposed coaxially within the outer tube 72. 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 72 is also fitted to the plunger shaft housing 86.

[035] The hydraulic damper assembly 70 comprises a threaded adjuster pin 52 for adjusting the operation of the hydraulic damper assembly 70. 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 element 55 of a restrictor valve 53 is provided which is employed to adjust the flow of hydraulic fluid in the damper assembly 70. The hole 34 permits insertion therethrough of a screwdriver or other tool to adjust the threaded adjuster pin 52.

[036] The inner tube 80, plunger head 17 and the plunger shaft housing 86 define an elongate inner chamber 90 through which the plunger shaft 60 extends. The inner chamber 90 is located within the inner tube 80. An elongate outer chamber 92 is located and defined between the outer tube 72 and the inner tube 80. The outer chamber 92 is annular and surrounds the inner chamber 90 which is cylindrical. At the plunger head 17 the inner chamber 90 and the outer chamber 92 communicate via the restrictor valve 53 comprising the needle valve element 55. At the plunger shaft housing 86 the inner chamber 90 and the outer chamber 92 communicate via at least one port (not shown) in the plunger shaft housing 86. 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.

[037] At the other end of the housing 2 a cylindrical end piece 56 is fitted into the housing 2 so as to close off a central 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 61 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.

[038] The hydraulic damper assembly 70 also comprises a piston 100, coupled to the housing 2 and slidable in a fluid-filled chamber 89 within the plunger 6. 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 piston 100 is mounted. A lock nut 112 is threaded onto the end of the second reduced diameter portion 102 so as to secure the piston 100 on the plunger shaft 60.

[039] The piston 100 divides the fluid-filled chamber 89 into two compartments 91,93, and the plunger 6 is movable relative to the piston 10. Such movement causes the fluid- filled chamber 89 to move relative to the piston 100 either in the first inward direction in response to movement of the tension member 14 inwardly of the housing 2 in a door closing motion, or in a second outward direction, opposite to the first inward direction, in response to movement of the tension member 14 outwardly of the housing 2 in a door opening motion. The fluid-filled chamber 89 comprises the inner chamber 90, defined within the inner tube 80 which functions as a cylinder for the piston 100, within which the piston 100 slides and the outer chamber 92 in fluid communication therewith via an adjuster 95 for adjusting a damping action of the hydraulic damping assembly 70 in a door closing motion. The adjuster 95 is located at one end of the fluid-filled chamber 89, and via at least one fluid return port (not shown), located at an opposite end of the fluid-filled chamber 89.

[040] The restrictor valve 53 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 70.

[041] The adjuster 95 of the hydraulic assembly 70 comprises the plunger head 17, constituting a head part of the plunger 6, which is connected to the tension member 14. The plunger head 17 comprises a first member 110 and a second member 112 which are assembled together. The first and second members 110, 112 of the plunger head 17 have respective opposite first and second transverse surfaces 114, 116 which are assembled together.

[042] A raised part 118 of the second member 112 extends above the second transverse surface 116. The first member 110 has a cavity 120 extending below the first transverse surface 114. The raised part 118 is received within the cavity 120. The raised part 118 has a cylindrical outer surface 122 and the cavity 120 has a cylindrical inner surface 124.

[043] The first and second members 110, 112 are assembled together by a threaded element 126. The threaded element 126 has a head portion 128 disposed at a rear face 130 of the second member 112 and a threaded end portion 132 threadably fitted within a threaded bore 134 of the first member 110.

[044] An outer surface 136 of the first member 110 is sealed to an inner surface 138 of the outer tube 72 by a first sealing element 140 and an outer surface 142 of the second member 112 is sealed to an inner surface 144 of the inner tube 80 by a second sealing element 146. The first and second sealing elements 140, 146 comprise O-ring seals.

[045] An elongate adjuster bore 148 extends through the first member 110 and the second member 112 and has a first open end 150 located at an outer surface 152 of the plunger head 17 and a second open end 154 which opens into the inner chamber 90. First and second portions 156, 158 of the elongate adjuster bore 148 are provided in the first and second members 110, 112 respectively.

[046] The first portion 156 of the elongate adjuster bore 148 comprises an internally threaded portion 160. The first portion 156 of the elongate adjuster bore 148 extends through the cavity 120. An annular recess 162 is, in the assembled configuration, provided the first member 110 and is adjacent to an inwardly-oriented end 164 of the internally threaded portion 160. The first portion 156 of the elongate adjuster bore 148 extends through the annular recess 162. The annular recess 162 contains an annular lip seal member 166, which preferably is composed of an elastomeric material. The annular lip seal member 166 has an inner sealing surface 170. The annular recess 162 containing the annular lip seal member 166 is formed when the raised part 118 is inserted into the cavity 120, since the raised part 118 is shorter in length than the cavity 120. The annular lip seal member 166 is disposed between the raised part 118 and an inner end 168 of the cavity 120 so that in the assembled configuration the annular lip seal member 166 is securely held in an immovable position within the plunger head 17.

[047] The second portion 158 of the elongate adjuster bore 148 also comprises a restrictor valve region 172, defining an annular internal valve surface 174, in fluid communication with the inner chamber 90. The second member 112 further comprises a transverse port 176 fluidically connecting the restrictor valve region 172 and the outer chamber 92. The transverse port 176 communicated with a bore portion 175 which has a larger radius than the restrictor valve region 172 and extends into the raised part 118 to define an open end 177.

[048] The adjuster 95 further comprises the threaded adjuster pin 52 which constitutes a rotatable elongate valve member received within the elongate adjuster bore 148.

[049] The threaded element 126, which joins together the first and second members 110, 112, has a longitudinal axis which is transversely offset from a longitudinal axis of the threaded adjuster pin 52. The longitudinal axis of the threaded element 126 and the longitudinal axis of the threaded adjuster pin 52 are each transversely offset from a central longitudinal axis of the adjuster 95.

[050] The threaded adjuster pin 52 comprises an externally threaded portion 180 which threadably engages the internally threaded portion 160 of the elongate adjuster bore 148, a sealable portion 182 which extends through, and is sealingly engaged by, the inner sealing surface 170 of the annular lip seal member 166, and the needle valve element 55 which extends along the restrictor valve 53. The externally threaded portion 180 is adjacent to one end 184 of the sealable portion 182 and an opposite end 186 of the sealable portion 182 is adjacent to the needle valve element 55. The annular internal valve surface 174 is cylindrical and the needle valve element 55 has an external frustoconical surface 188 which faces, and is spaced from, the annular internal valve surface 174. The external diameter of the external frustoconical surface 188 decreases in the first inward direction. The external diameter of the sealable portion 182 is greater than the largest external diameter of the needle valve element 55.

[051] Rotation of the threaded adjuster pin 52 is configured to adjust a maximum rate of fluid flow between the inner and souter chambers 90, 92 though the transverse port 176 and the restrictor valve region 172 of the restrictor valve 53.

[052] The inner sealing surface 170 of the annular lip seal member 166 is circular and the sealable portion 182 has a cylindrical external surface 190 which is engaged by the inner sealing surface 170. Apart from the annular lip seal member 166, no other seal or seal member is provided between the threaded adjuster pin 52 and the elongate adjuster bore 148. The sealable portion 182 extends through the cavity 120 and into the bore portion 175, and the needle valve element 55 is received in the restrictor valve region 172.

[053] The piston 100, which is mounted on the plunger shaft 60, preferably has the structure described in WO-A-2011/051317. The piston 100 preferably comprises a valve mechanism 101 which opens to permit relatively free movement of the fluid from one compartment to the other compartment when the plunger is moved relative to the piston in the second outward direction, opposite to the first inward 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 inward direction.

[054] The piston 100 can move between a sealed position and an unsealed position, as described in WO-A-2011/051317.

[055] In the sealed position, which is achieved when the hydraulic fluid pressure acts in a direction from left to right in the drawings of FIGs. 1 and 2 during closing of the door closer, in which the assembly of the outer and inner tubes 70, 80 moves to the right in FIGs. 1 and 2 along the plunger shaft 60, the fluid pressure urges the piston 100 into a sealed position. The closing movement of the door closer resulting from the spring bias is damped by the restrictor valve.

[056] However, in the unsealed configuration, the piston 100 has been urged by hydraulic pressure in a left hand direction in FIGs. 1 and 2, which 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 FIGs. 1 and 2 along the plunger shaft 60. Hydraulic fluid within the inner chamber 92 can flow through the valve assembly 101 in the piston 100. There is substantially no seal in the piston 100 in this configuration. The opening movement, against the spring bias, is substantially unrestricted by the piston 100 and is not damped by the restrictor valve 53.

[057] An accumulator 196 comprises an elongate annular 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 196 comprises a body of foamed plastics or rubber material, comprising a closed cell foam structure, such as neoprene. The accumulator 196 is spaced from the piston 100 by at least one rigid spacer 198, e. g. of nylon, which prevents trapping of the accumulator 196 in any gap between the piston 100 and the inner tube 80. [058] The present invention provides a concealed door closer that can comply with BS EN 1154 1997. 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 1154 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 1154 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.