You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates to a valve which is suitable for use with a hydraulically activated device such as a rock prop employed in an underground location. 
         [0002]    In one type of rock prop water under pressure is used to set the prop so that it is brought to an operative condition as soon as possible at the time of installation. Typically the prop is positioned between a foot wall and an opposed hanging wall. After installation, if closure of the hanging wall towards the foot wall takes place, then the pressure of water inside the prop is increased and, to accommodate the hanging wall movement, water is released from the prop at a controlled rate. 
         [0003]    In order to set a prop in the aforementioned manner water is introduced through a filler valve into an interior of the prop. When the source of pressurised water is disconnected from the prop interior, the filler valve automatically closes. It is possible to use the filler valve as a release valve to allow water under pressure to escape from the prop interior. Alternatively, a release valve designed for the purpose, is used. 
         [0004]    Arduous conditions exist underground. Although filters and similar mechanisms can be used to remove particulate material from water which is to be used with a prop, it is quite possible that unwanted particles can be entrained in the water which is introduced into a prop. The problems which are posed by these particles when the prop is being set can normally be overcome. However, when a prop is under pressure and closure takes place then small quantities of water must be allowed to escape at a controlled rate from the prop to cater for the closure. The presence of foreign particles in the water escaping from a prop can adversely affect the functioning of a pressure release valve. For example, if a particle is lodged between a valve member and a valve seat then the valve member would normally not be able to seal and water would escape continuously from the prop which then would not be capable of exhibiting its designed load-bearing function. 
         [0005]    An object of the present invention is to provide a valve which, to some extent at least, addresses the aforementioned situation. 
       SUMMARY OF INVENTION 
       [0006]    The invention provides a valve for use with a hydraulically activated device, wherein the valve includes a housing, a bore through the housing, the bore having an inner surface, an inlet to the bore, and an outlet from the bore, a tubular valve member which is made from a resiliently deformable material and which is located in the bore, the tubular valve member including an outer surface, a first end, an opposed second end, and a passage through the valve member from the first end to the second end, a first seal between the first end of the tubular member and an opposed section of the inner surface of the bore, a second seal between the second end of the tubular member and an opposed section of the inner surface of the bore, and a filler arrangement, connected to the housing, to introduce a gas under pressure into a volume between the first seal and the second seal and between the outer surface of the tubular valve member and part of the opposed inner surface of the bore. 
         [0007]    The filler arrangement may comprise a one-way valve. 
         [0008]    The inlet to the bore may be used to introduce a liquid e.g. water under pressure into an interior of the device, e.g. a prop, to which the valve is connected. The outlet may be connected to the device, i.e. the prop, opposing an opening through a wall of the prop. 
         [0009]    A retention device, e.g. a circlip, may be positioned inside the bore to restrict movement of the tubular valve member towards the inlet. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0010]    The invention is further described by way of example with reference to the accompanying drawing which illustrates from one side and in cross-section a valve according to one form of the invention. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
       [0011]    The accompanying drawing illustrates from one side and in cross-section a valve  10  according to the invention, which is connected to a wall  12  of a hydraulically activated rock prop (not shown in detail). 
         [0012]    The valve  10  includes a housing  14  through which extends a bore  16 . The bore has an inner surface  18 , an inlet  20  and an outlet  22 . The housing is attached in any suitable way to the wall  12 , for example by means of welding  24 . The outlet  22  opposes an opening  26  in the wall so that the outlet is thereby placed in communication with an interior of the prop. 
         [0013]    The housing  14 , in an outer surface adjacent the inlet, is formed with a circumferentially extending slot  30 , as is known in the art, so that a connection device, not shown, can be coupled to the housing. The connection device is at an end of a hose or conduit which extends from a pressurised source of water, not shown. This aspect is known in the art and therefore is not further described herein. 
         [0014]    A tubular valve member  40  is located inside the bore  16 . The valve member is made from a resiliently deformable material e.g. polyurethane or rubber. A passage  42  extends through the tubular valve member from a first end  44  to a second end  46 . 
         [0015]    A first seal  48  is coupled to the first end and defines a sealing interface between the inner surface  18  of the bore and the tubular valve member  40 . Similarly a second seal  52  is engaged with the second end and defines a sealing interface between the inner surface  18  and the tubular valve member. 
         [0016]    The first seal  48  has a passage  60  which extends through the seal and an adjacent tubular spigot  62  which extends into the passage  60 . The second seal  52  is similar to the first seal and has a passage  66  which extends through the seal and an adjacent tubular spigot  64  which extends into the passage. Thus, flow of a liquid can take place through the passage  66  into the passage  42  and then into the passage  60 . 
         [0017]    A one-way filler valve  70  is connected to a side of the housing at a location which is between the first and second ends  44  and  46 . 
         [0018]    In use of the valve  10  a pressurised gas is introduced through the one-way filler valve  70  into a volume  72  which is defined between an outer surface of the tubular valve member  40  and an opposing part of the inner surface  18  of the bore and which is located between the first end  44  and the second end  46  of the tubular valve member. The pressure of the gas is sufficiently high to cause the tubular valve member to collapse so that the passage  42  between the first and second ends is effectively sealed. 
         [0019]    The inlet  20  can be connected to a source of pressurised water, in the manner which has been described and water can then be passed through the inlet  20 , and through the passage  66 , in the second seal. If the incoming water has a pressure which is sufficiently high then the tubular valve member  40  is forced to move so that the passage is opened and water flows through the passage  42  in the valve member to the passage  60 , to the outlet  22  and then into the opening  26  into the interior of the prop. 
         [0020]    If the valve  10  is disconnected from the pressurised water source the gas pressure in the volume  72  is sufficiently high to cause the valve member to collapse and immediately seal. 
         [0021]    If the pressure inside the prop increases above a designed limit, for example if closure takes place of a hanging wall and a foot wall between which the prop is installed, then an increased pressure is exerted at the outlet of the valve member. The pressure increases as the degree of closure increases and a point is reached at which the tubular valve member is forced open to allow a quantity of water to escape through the passage  42  to the surrounding environment. As the pressure reduces inside the prop the force exerted by the pressurised gas in the volume  72  causes the tubular valve member to close, again. 
         [0022]    A principal benefit of the invention lies in the fact that the valve member is made from a resiliently deformable material such as rubber, polyurethane or the like. These materials are exemplary only and are non-limiting. If a particle carried by water exiting the prop is in the passage  42  when the tubular valve member closes then, because of the nature of the material from which the member is made, it is possible for the material to deform and accommodate the particle. It is unlikely that the particle, in itself, will cause the sealing action of the valve member to be impaired. 
         [0023]    If the pressure in the prop is again increased then, in the manner described, the tubular valve member is opened and water can flow from the prop. In this event it is likely that the particle previously trapped inside the passage  42  would be flushed to the surrounding environment.

Summary:
A valve includes a flexible tube in an enclosure which is filled with pressurized gas which collapses the tube and wherein a fluid, applied at either end of the tube, can open the tube if the pressure of the fluid is sufficiently high.