GB2254653A - Door closer. - Google Patents

Abstract

A door closer, intended to be recessed into a floor for use with a swing door, has a main bore (11) in which is slidable a piston (12) which divides the bore (11) into two pressure fluid chambers (13,14), the piston being biased by a spring (15) to move a closer shaft, which is rotatable, in use, in response to the opening of a door with which the closer is associated. The closer has a housing (10) in which is only a single, longitudinal fluid flow passage (16) communicating with the chamber (13) by respective throttled passages (18, 19:21, 22) and with chamber (14) by passage (17). By providing either a further throttled passage (31) between the longitudinal passage (16) and fluid chamber (14) together with a poppet valve (34) and a pressure relief valve (46), or a poppet valve together with a solenoid, the basic closer with latch action closing can easily be adapted to provide hydraulic hold open, delayed action closing and electro-hydraulic hold open functions with only a single longitudinal fluid flow passage. <IMAGE>

Description

DOOR CLOSER This invention relates to a door closer having a rotatable closer shaft, intended for connection to a movable door, and energy storage means which are charged and discharged upon rotation of the closer shaft as the door is open and closed respectively, in use. One form of such a door closer is a floor spring which is recessed into a floor and controls movement of a swing door.

U.K. Patent specification no. 2052622 relates to a floor spring and has a housing which has two diametrically opposed, longitudinally extending passages therein for transferring pressure fluid from a contracting pressure fluid chamber at one side of a piston to an expanding pressure fluid chamber at the opposite side of the piston as the door closes, in use.

In order to be able to provide various hold-open positions of the door, each longitudinal passage has a throttle means therein. Whilst the door closer is satisfactory, in use, its manufacture does require the production of two longitudinal flow passages, each with associated transverse bores communicating it with the chamber at opposite sides of the piston.

An object of the invention is to provide a door closer which is improved compared to the prior art.

According to the invention there is provided a door closer comprising a housing, a closer shaft extending from the housing and being rotatable, in use, in response to the opening of a door with which the door closer is associated, a piston slidable within a main bore in the interior of the housing, the piston moving in one direction in response to rotation of the closer shaft as the door is opened, in use, and charging energy storage means in the housing, the energy storage means releasing stored energy to move the piston in its opposite direction when door closing occurs, the piston dividing the main bore into two pressure fluid chambers, and there being a single longitudinal fluid flow passage formed in the housing, the fluid flow passage extending between the two fluid chambers.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a fragmentary, longitudinal section through a door closer of the invention, Figure 2 is a section on the line 2-2 of Figure 1, Figure 3 is a view like Figure 1 of an alternative embodiment of the invention, and Figure 4 is a view like Figures 1 and 3 of a still further embodiment of the invention.

Referring to Figures 1, 3 and 4, each of the respective door closers shown therein is of the kind to be recessed into a floor and is intended, for example, for use with a swing door. Each door closer has a housing 10 which is substantially rectangular in plan and in which is formed a cylinder bore 11, which contains a pressure fluid, for example oil. Sealingly disposed for sliding movement in the bore 11 is a piston 12 which divides the bore 11 into two pressure fluid chambers 13, 14 respectively. A helical compression spring 15 is contained in chamber 13, its one end bearing against the piston 12 while its other end is supported against a partially closed end of the bore, not shown. A connecting rod (not shown) extends within the spring 15 and couples the piston to a longitudinally movable slide.

Formed in the slide is a longitudinally extending slot through which passes a rotatable door closer shaft. The arrangement of connecting rod, longitudinally movable slide and door closer shaft is, with other associated components, of conventional form, such as shown for example in British Patent specifications nos. 1259030 and 2052622, and will thus not be further described. As is well known in the art, the closer shaft is connected directly or indirectly to the door so that opening of the door causes rotation of the closer shaft, which, via a cam causes longitudinal movement of the slide and associated rod, with the result that the piston is moved in the cylinder bore 11 to compress the spring 15 which acts as an energy storage means to tend to return the door to its closed position on release of the opening force.

For each of the door closers shown in Figures 1, 3 and 4 respectively, there is in the housing 10 a single, longitudinally extending fluid flow passage 16, which is, in these examples, parallel to the axis of the bore 11.

At its one end it is joined by a short transverse passage 17 leading into the chamber 14. At it other end the passage 16 is connected to a short transverse passage 18 communicating with the chamber 13 by way of an enlarged stepped bore 19 which extends to the outside of the housing. Contained within the bore 19 is a throttling means 20 which can be adjusted to restrict or prevent fluid flow from the passage 16 into the chamber 13, as will be described. At a position along its length nearer the end of the passage 16 which has the throttling means 20, is a further enlarged stepped bore 21 interposed between the passage 16 and a further short transverse passage 22 leading to the cylinder bore 11. The bore 21 also extends to the outside of the housing and contains a further throttling means 23 of the same form and the throttling means 20 in the bore 19.The passage 22 is positioned so that it is only uncovered by the piston 12 to put it into communication with the chamber 13 during the last few degrees of closing of the door, so that if the bore 21 is less restricted by the throttling means than the bore 19, fluid will flow out through the passage 22 into the chamber 13 at the end of the closing of the door, thereby providing a latching effect, to be described in detail hereinafter.

Contained within a bore in the piston 12 is a feed valve 24 which is normally sealed on its valve seat by means of a light compression spring 25. When fluid pressure increases in chamber 13, the valve 24 is lifted off its seat to allow fluid to flow into the chamber 14.

The piston also has a central bore in which is received a safety valve 26, in which a ball 27 is held on its seat by a spring 28. Although normal exhaust of fluid from chamber 14 to chamber 13 takes place by way of the passage 16, excessive pressure in the chamber 14 as a result of the door being forced in the closing direction, can be relieved by way of the safety valve 26 by means of the ball 27 being lifted off its seat by said excess pressure in the chamber 14 being greater than the force of the spring 28. Fluid can thus flow directly from the chamber 14 to the chamber 13.

The door closer structure so far described can be seen, from Figures 1, 3 and 4, to be common to each of the three embodiments of the invention. In particular it is to be noted that there is only a single fluid flow passage within the door closer housing or body. Despite this, as will be described in relation to the embodiments of Figures 3 and 4, it is still possible to provide various hold-open/delayed action features, which, with prior art devices, have required additional and sometimes more complicated fluid flow passages within the housing or body of the door closer. Clearly having to provide only a single longitudinally extending fluid flow passage in the housing or body it is advantageous in relation to both ease and cost of manufacture.

Having described the structure of the door closer which is common to all three of the illustrated embodiments, each embodiment will now be described in detail.

Figure 1 is a basic fire door unit and has as its purpose the provision of means whereby a door may be automatically closed, the rate of door closing being adjustable and providing means by which, in the latter stage of the closing, the door can be accelerated to overcome door latch resistance. This is suitable for both single action and double action doors which may be sited to prevent the spread of fire or smoke and are thus required to remain closed in this event.

When a door is opened, the piston 12 is moved away from an end plug 29 which sealingly closes the end of the cylinder bore 11 remote from the door closer shaft. This movement compresses the spring 15. Simultaneously the pressure of the damping fluid in chamber 13 is slightly raised and flows freely into chamber 14 via the feed valve 24 which is opened against its spring 25.

On release of the door, the spring 15 returns the piston towards the end plug 29, with this movement of the piston being transmitted via its connecting rod and longitudinal slide to the door closer shaft so as to move the door towards its closed position. At this point the feed valve 24 is closed by its spring 25 and the pressure of the fluid in chamber 14 is raised by the movement of the piston towards the end plug 29. As a result of this increased pressure fluid flows from chamber 14 into chamber 13 through passage 16, at a rate dependent upon the setting of the throttling means 20. In the course of its movement towards the closed position, the door can be accelerated during the last part of its closing cycle, for example for its last 150 of its closing movement.

This is effected by opening the further throttling means 23. The further passage 22 is blocked by the piston at door open angles greater than approximately 15 , but becomes exposed to chamber 13 when the rear face of the piston moves to the position shown in Figure 1 in the closing cycle. Fluid is thus able to bypass the throttling means 20 and exhaust into chamber 13 at a faster rate set by the further throttling means 23, thereby causing a latching of the door.

Should the door be forced in the closing direction by either excessive wind pressure or user abuse, the fluid pressure in chamber 14 is increased. The safety valve 26 will open in this event to relieve this excess pressure, allowing fluid to flow directly from chamber 14 to chamber 13 through this valve. Excessive chamber pressures and undue working stresses which might otherwise occur in the mechanism and the door mountings are thus prevented.

Turning now to the embodiment in the invention shown in Figure 3, it can be seen that as compared to the embodiment of Figure 1, there is a different end plug and that there is a still further throttling means between the fluid flow passage 16 and a passage communicating it with the chamber 14.

The still further throttling means 30 is of the same form as the means 20 and 23 and is between the flow passage 16 and a still further short transverse passage 31 in communication with chamber 14 just ahead of an end plug 32 closing the cylinder bore 11.

The end plug 32 has threadedly engaged therein a central valve housing 33 for a sleeve-like poppet valve 34. Towards one end of the poppet valve 34 it is externally stepped to provide a shoulder for one end of a compression spring 35, the other end of which is received against a valve housing sealing plug, thereby biasing the poppet valve 34 in a direction away from the end plug 32.

The exterior of the end of the poppet valve at which the compression spring 35 is received has a seal in sliding contact against the inside of the housing 33.

Approximately along mid-way along its length the exterior surface of the poppet valve 34 is stepped to provide an angular shoulder for an annular seal 36. Spaced slightly away from the seal 36 towards the end of the valve 34 remote from the end plug 32 is a radial through bore 37 which is in communication with a central hollow passage 38 extending through the poppet valve from its end remote from the plug 32. This end has a slot 39 around part of its periphery to allow fluid flow from the chamber 14 into the passage 38 even when axial entry into the passage 38 is prevented, as will be described.Figure 3 shows the position of the poppet valve at or near the end of the closing of the door where the seal 36 has been moved back off its seat 40 provided at an inner end of the housing 33, defining a variable volume chamber 41 which can receive fluid flowing through the bore 37, the chamber including clearance around part of the poppet valve exterior rearwards from its seal 36.

A radial through bore 42 extends through the housing 33 from the chamber 41 to an annular external groove 43 of the valve housing. The bore 42 is positioned so that fluid can flow through it from the chamber 41 up until the time when the seal 36 engages on its seat 40. The groove 43 is in communication with a radial drilling 44 extending through the end plug 32 into communication with an annular groove 45 in the external periphery of the plug 32 which is sealingly engaged in the bore 11 by O-rings at opposite sides of the groove 45. The passage 17 is in direct communication with the groove 45 so that when the seal 36 is off its seat 40, fluid can always flow from the chamber 14 to the passage 17 and then to the fluid flow passage 16.

As described, the spring 35 urges the poppet valve in a direction away from the end plug 32, and, as shown in Figure 3, this causes engagement of the end of the poppet valve against an annular flange of the safety valve 26 in the piston 12, when the piston is at or near the end of the cylinder bore 11 closed by the end plug 32. The end of the poppet valve 34 continues to be forced by the spring 35 to engage the safety valve 26 as the door is opened and the piston moves to the left as viewed in Figure 3. However, as this movement of the piston takes place, the poppet valve slides in its housing 33 until the seal 36 engages its seat 40, whereupon further leftwards movement of the poppet valve is prevented, and its end is then disengaged from the safety valve 26 as the piston continues to move further to the left. Disengagement of the poppet valve from the safety valve 26 occurs at a particular angle of door opening, and this can be adjusted by screwing the housing 33 further into or out of the end plug 32. This angle is typically between approximately 70" and 105 .

Fitted in an off-central bore in the end plug 32 is an pressure relief valve 46 which has a passage 47 in communication with chamber 14, this passage normally being closed by a spring loaded ball part 48 of a piston member 48A. The ball part, piston member and loading spring are all contained in a hollow sleeve part of the valve 46 which has an opening at its end remote from the chamber 14. The valve has a cross-drilling 46A to communicate the interior of the sleeve part of the valve with the bore in which the valve 46 is sealingly secured.

This bore is in communication with the drilling 44, so that in circumstances to be described, pressure can be relieved from the chamber 14 by fluid flow which once established is maintained. The fluid flow is through the passage 47, the hollow sleeve part of the valve 46, the cross-drillings 46A and 44, the latter of which is in communication with the passage 17.

Full operation of this second embodiment of a door closer of the invention will now be described.

The functions previously described for the door closer shown in Figures 1 and 2 apply equally to the embodiment shown in Figure 3, with the further functions of hold-open and delayed action closing being added. The different functions are incorporated in this single main fluid flow passage arrangement and are selectable by means of the setting of the still further throttle means 30.

When it is required for the door automatically to be held open beyond a certain predetermined opening angle, this angle is firstly set by adjustment of the poppet valve housing 33 as described above. Additionally the still further throttle means 30 is set fully closed, thereby preventing fluid flow from the chamber 14 via the passage 31 into the main fluid flow passage 16. This arrangement, combined with other functions to be described hereinafter, allows the door to be held open beyond the angle chosen, whilst if the door is not opened beyond the chosen set angle, it will close in the normal manner.

For a delayed action closing, the still further throttle means 30 is set partially open to allow fluid flow from the chamber 14 into the passage 16 via the passage 31. This, combined with other functions to be described hereinafter, allows the delayed closing zone to end at any door open angle between approximately 700 and 105 , this again being adjustable by means of the valve housing 33. The door will close in the normal manner if not opened beyond the chosen set angle, but will initiate a delayed closing zone if pushed beyond this set angle.

The period of delayed closing is dependent upon the angular distance by which the door is opened beyond the chosen set angle and the setting of the still further throttle means 30 which controls how quickly fluid can exhaust from the chamber 14 past it into the passage 16.

General operation of the unit will now be described.

As the door is opened, the poppet valve 34 slides in its valve housing 33 as it is forced by its spring 35 against the safety valve 26 which is itself moving to the left, as shown in Figure 3, with the piston 12. As described, the poppet valve remains in contact with the safety valve 26 until the poppet valve seal 36 engages on its seat 40.

If the degree of door opening is below the predetermined chosen angle referred to above, leftwards movement of the piston will cease before the end of the poppet valve 34 disengages from the safety valve 26.

Accordingly, during opening, fluid flows from the chamber 13 to the chamber 14 through the feed valve 24 in the same manner as with the Figure 1 embodiment. Once the opening force on the door is removed, the spring 15 forces the piston 12 to the right, and fluid in chamber 14 can exhaust through the poppet valve. Thus fluid exhausts through slot 39, bore 37, chamber 41, bore 42, groove 43, drilling 44, and groove 45, into passage 17 and main fluid flow passage 16. It is irrelevant whether or not the still further throttle means 30 is open or closed. Thus the door closes under the influence of the spring 15, with the already described latching facility being possible by use of the further throttling means 23.

Opening of the door beyond the predetermined set limit causes the poppet valve seal 36 to engage on its seat 40 and for the end of the poppet valve simultaneously to disengage from the valve 26. Further opening of the door beyond this point is merely opposed by the force of the spring 15, fluid still flowing from chamber 13 through valve 24 into chamber 14. Once the opening force on the door is removed, the piston 12 will be urged to the right, as viewed in Figure 3 by the force of the compressed spring 15. Fluid in chamber 14 cannot exhaust through the poppet valve, since the bore 37 is now sealed off from the chamber 41, and pressure of fluid in chamber 14 rises.

If at this stage the still further throttle means 30 is closed, fluid cannot exhaust from chamber 14 and the door is held open. However, if the means 30 is set partially open, fluid will flow from chamber 14 past said means 30 into the passage 16 and exhaust into chamber 13 via the throttling means 20 and passage 18. In this instance the means 30 is normally set more closed than the means 20 and since both valves are at this stage in the same fluid flow path, the rate of door closing is more influenced by the means 30 which is providing the delayed (slow closing) function.

The door continues to close slowly under the control of the fluid flow through the means 30 until the end flange of the safety valve 26 contacts the end of the poppet valve. At this point the poppet valve is moved along its housing 33 so that its seal 36 moves off its seat 40 thus again opening the exhaust passage through the poppet valve and end plug from chamber 14. The means 30 is thus now bypassed and the fluid flow becomes controlled by the throttling means 20 alone, this being set to allow a normal door closing rate, with again the possibility of a final latching by opening of the further throttling means 23.

Should the door user wish either to release the door from a hold-open position, or to accelerate the door through its slow closing zone, this may be achieved by pulling or pushing the door towards its closed position.

Such applied force causes a further pressure rise in chamber 14 which will cause the ball part 48 of piston member 48A to move off its seat, exposing the piston member 48A to this pressure. As the piston member is of a larger area in comparison with the initial area of the ball part exposed to the pressure whilst on its seat, the piston member can be further disturbed by a lower pressure. Accordingly if the applied force is now removed, the normal pressure in chamber 14 continues to move the piston member until the cross-drilling 46A communicates with the sleeve interior allowing exhaust of fluid through the relief valve 46 into passage 16 and thence into chamber 13 under the control of the throttling means 20.

The relief valve 46 is set to relieve pressure at a level lower than the main safety valve 26. This is to allow the door user to override the hold-open or delay functions by application of a reasonable force. The main safety valve 26 only opens if excessive pressure is produced in chamber 14 at any door angle. Accordingly it can be seen that by the introduction of only a single additional throttling means a single main fluid flow passage in the body can be used to provide various holdopen and delayed closing functions in conjunction with one or more valves in the end plug.

The door closer embodiment shown in Figure 4 uses the same single fluid flow passage 16 with throttling means 20 and 22 as the Figure 1 embodiment, and additionally uses the same piston arrangement 12 with feed valve 24 and safety valve 26. Thus the only difference from the Figure 1 arrangement concerns the replacement of end plug 29 by a different end plug 49.

This end plug 49 is sealingly engaged in the open end of the cylinder bore 11, with an external annular groove 50 being provided in the end plug, this groove having a substantial extent in a direction parallel to the axis of the bore 11. The groove 50 is in communication with the transverse passage 17. In an off-centre bore 51 in the end plug 49 is disposed a poppet valve 52 of a similar form to the poppet valve 34 of Figure 3. The poppet valve 52 has an annular seal 53 at an external shoulder and seats against a facing annular part 54 of end plug 49 under the action of a compression spring, as with the Figure 3 embodiment. This time instead of engaging the safety valve 26, the end of the poppet valve engages a washer 55 generally at the outlet of the feed valve 24.

A chamber 56 is defined between the seal 53 and its seat 54 and a bore 57 leads from the inside of the poppet valve into the chamber 56 with a further bore 58 leading from chamber 56 into the groove 50. Clearly the angle of door opening at which the fluid can no longer flow through the sealed closed poppet valve, i.e. the angle of hold-open of the closer, can be fixed or can be arranged to be variable, for example, by varying the stop position of the end plug 49 in the cylinder bore, or by other suitable means.

The end of the plug is provided with a solenoid coil 59 with a solenoid core 60 being moveable, when the solenoid is actuated, by magnetic influence towards a solenoid pole piece 61. The solenoid core acts on a push rod 62 which has a head 63 to act upon a ball 64 to move it onto a seating in a chamber 65 which is connected by a passage 66 to the groove 50. When on its seat, the ball 64 closes a passage 67 in communication with the chamber 14.

The functions previously described for the operation of the Figure 1 embodiment apply equally to this unit and the further function of electro-hydraulic hold-open is added. This unit provides means whereby a door may be held open beyond an angle of, for example, approximately 750 but be automatically released and closed from this position in the event of fire. Incorporated in the unit is a solenoid operated valve which when energised causes the door to be held open and when deenergised allows the door to close. The electrical power supply to the solenoid operated valve is normally interfaced with a fire alarm system, such that when this is signalled into the alarm state, it causes the power supply to be interrupted.

Tne seat for the ball 64 is interposed in the primary fluid flow path which connects the pressure chamber 14 via passages 66 and 67 and annular groove 50 to the main fluid flow passage 16.

When voltage is applied to the solenoid coil, the solenoid core 60 is moved as described towards the solenoid pole piece 61 thereby moving the push rod so that its head forces the ball 64 onto its seating. The sustained force from the solenoid holds the ball in this position and closes the above described primary fluid flow path.

As with the poppet valve of Figure 3, the poppet valve 52 provides a fluid flow path, this time a secondary fluid flow path connecting the pressure chamber to the passage 16 by way of bore 57, chamber 56, bore 58 and groove 50. This flow path bypasses the primary fluid flow path when the latter is closed and prevents the door from being held open of angles less than approximately 75". The poppet valve seal 53 seats on part 54 if the door is opened beyond 750, and if the solenoid valve is energised, fluid is thus unable to exhaust from chamber 14, thus causing the door to be held open.

Full operation of the unit will now be described.

As the door is opened fluid flows from the chamber 13 into chamber 14 through the feed valve 24. As the piston moves to the left, the poppet valve slides in its bore in the end plug 49 with its end engages against the washer 55. This engagement is retained until a door open position is reached where the poppet seal 53 moves onto its seat. This closes a secondary fluid flow path, preventing exhaust from the chamber if the solenoid is actuated. If the door is only opened below the predetermined set angle, the door can close as normal even if the solenoid is energised.

Once this secondary flow path is closed, further movement of the poppet valve is prevented and continued opening of the door disengages the poppet valve from the washer 55. Fluid continues to flow through the feed valve 24 and fluid in chamber 14 increases in volume whilst being unable to exhaust. Accordingly, when the door opening force is removed the door remains at the angle to which it has been opened.

The door may be released from its held-open position by either applying force on the door in its closing direction or by interrupting the voltage to the solenoid coil. Both means effectively initiate opening of the primary fluid flow path and common door closing functions.

Applying force to close the door raises the standing pressure in chamber 14 until a pressure is reached which overcomes the force applied by the solenoid to the ball 64. The ball is thus moved off its seat by this increased pressure and fluid flows from the chamber via the primary fluid flow path into the passage 16 and exhausts into the chamber 13 via the throttling means 20.

The door closes at a rate dependent upon the setting of the throttling means 20 which restricts the fluid flow.

Alternatively interruption of the applied voltage to the solenoid coil removes the magnetic force on the core, thus releasing the pressure holding the ball 64 in position. The standing fluid pressure in chamber 14 can now move the ball 64 off its seat allowing fluid flow and door closing as previously described.

In both cases, the secondary fluid flow path is re-opened when the washer 55 contacts a poppet valve end.

This causes no effective change in the closing action since the secondary flow path is in parallel with the primary flow path and neither of these bypass the means 20.

The safety valve 26 will operate, as described with the embodiments of Figures 1 and 3, if there is an excessive, and thus potentially damaging, build up of pressure in chamber 14, fluid thus being exhausted from chamber 14 directly into chamber 13 past the ball 27.

Thus it can be seen that by simple use of differently constructed end plugs a single main fluid flow passage way in the body is sufficient to allow substantially the same body to be used with three different embodiments of door closer, the only additional manufacturing operation being that required to provide for the still further throttling means 30 and associated passages. Manufacture is thus easier and less expensive as compared to prior art devices.

Claims (20)

1. A door closer comprising a housing, a closer shaft extending from the housing, and being rotatable, in use, in response to the opening of a door with which the door closer is associated, a piston slidable within a main bore in the interior of the housing, the piston moving in one direction in response to rotation of the closer shaft as the door is opened, in use, and charging energy storage means in the housing, the energy storage means releasing stored energy to move the piston in its opposite direction when door closing occurs, the piston dividing the main bore into two pressure fluid chambers, and there being a single longitudinal fluid flow passage formed in the housing, the fluid flow passage extending between the two fluid chambers.

2. A door closer as claimed in Claim 1, wherein the single, longitudinal flow passage is in communication with the one of the two fluid chambers which expands in volume when the door closes, in use, by means of a throttled flow passage.

3. A door closer as claimed in Claim 2, wherein the single, longitudinal flow passage is communicable with said one fluid chamber at an end of the closing of the door, in use, by means of a further throttled flow passage.

4. A door closer as claimed in any one of the preceding claims, wherein the piston has a feed valve for flow therethrough, in use, from said one fluid chamber to the other fluid chamber, as the door is opened.

5. A door closer as claimed in Claim 4, wherein the piston has a safety valve to allow flow therethrough, in use, from said other fluid chamber to said one flow chamber should excessive pressure occur in said other fluid chamber.

6. A door closer as claimed in any one of Claims 2 to 5, wherein a still further throttled passage extends between said single longitudinal flow passage and other of the two fluid chambers, the throttle being adjustable to permit or to prevent flow through said still further throttled passage.

7. A door closer as claimed in Claim 6, including a poppet valve slidable in a housing, the poppet valve being biased towards a closed position where flow through it is prevented, but being movable away from its closed position by movement of the piston in a direction to expand the volume of said one fluid chamber, to allow flow from said other fluid chamber to said one fluid chamber.

8. A door closer as claimed in Claim 7, wherein said poppet valve is moved to its closed position when the door is opened, in use, beyond a predetermined angular set limit, removal of the door opening force resulting in the door being held open beyond said set limit if said throttle is set to prevent fluid flow through said further throttled passage, and resulting in closing of the door, if said throttle is set to permit flow, the closing being at an initial rate until said set limit is reached, whereupon said poppet valve opens so that the door closes at an increased rate.

9. A door closer as claimed in Claim 8, whereupon the poppet valve housing can be adjusted to alter said angular set limit of the door.

10. A door closer as claimed in Claim 8 or Claim 9, including a pressure relief valve operable to relieve pressure in said other of the fluid chambers if force is applied to the door, in use, to move it to its closed position prior to it reaching said set limit.

11. A door closer as claimed in Claim 10, wherein once said pressure relief valve has initially operated, it will continue to exhaust said other of the fluid chambers prior to the door reaching said set limit, even if said force is removed.

12. A door closer as claimed in Claim 10 or Claim 11, wherein the pressure relief valve is set to relieve pressure at a level lower than a or said safety valve of the piston.

13. A door closer as claimed in any one of Claims 2 to 5, including a slidable poppet valve biased towards a closed position where flow through it is prevented, but being movable from its closed position by movement of the piston in a direction to expand the volume of said one fluid chamber to allow fluid flow from said other fluid chamber to said one fluid chamber.

14. A door closer as claimed in Claim 13, including a solenoid actuable to open or close a flow path from said other fluid chamber to said one fluid chamber via said longitudinal flow passage.

15. A door closer as claimed in Claim 14, wherein said poppet valve is moved to its closed position when the door is opened, in use, beyond a predetermined angular set limit, removal of the door opening force resulting in the door being held open beyond said set limit if the solenoid is energised to prevent flow through said flow path, and resulting in closing of the door if the solenoid is not energised or is de-energised after said holding open of the door.

16. A door closer as claimed in Claim 15, wherein the solenoid has a core which acts to force a ball onto a seat to close said flow path when the solenoid is energised, application of sufficient force to the door in its closing direction when it is being held open, causing generation in said other fluid chamber of a pressure sufficient to move the ball against the force of the solenoid core, thereby opening said flow path and causing closing of the door.

17. A door closer as claimed in any one of Claims 14 to 16, wherein the solenoid has an electrical power supply which is interfaced with a fire alarm system, so that when the alarm is actuated it causes an interruption to the power supply thereby causing the solenoid to be de-actuated to open said flow path.

18. A door closer as claimed in any one of Claims 10 to 12, wherein the poppet valve housing and the pressure relief valve are in an end plug of said main bore of the door closer.

19. A door closer as claimed in any one of Claims 14 to 17, wherein the poppet valve and the solenoid are in an end plug of said main bore of the door closer.

20. A door closer substantially as hereinbefore described, with reference to and as shown in Figures 1 and 2, or Figures 2 and 3 or Figures 2 and 4 of the accompanying drawings.