GB1601963A - Method of assembling a pneumatic piston and cylinder assembly - Google Patents

Description

(54) A METHOD OF ASSEMBLING A PNEUMATIC PISTON AND CYLINDER ASSEMBLY (71) We, AUTOMATIVE PRODUCTS LIM ITED, a British Company, of Tachbrook Road, Leamington Spa, Warwickshire, CV3 1 3ER, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to pneumatic piston and cylinder assemblies particularly, but not exclusively, for use in cable tensioning devices in electric railway overhead wire systems. A known cylinder assembly of this type is described in British Patent Specification No. 1,137,081. The cylinder assembly described in that specification uses an annular chamber which is kept filled with liquid to maintain the ramrod seal effective for long periods of service, the same liquid being used also to vary the maximum volume of a charge of gas used to operate the cylinder assembly. These cylinder assemblies have enjoyed considerable commercial success but in the installation procedure there is a disadvantage in that some of the pressurised gas dissolves in the oil. Hence a long stabilisation period is required to ensure that the gas pressure is correct when installed.

It is an object of the invention to provide a pneumatic piston and cylinder assembly which does not require a long period of stabilisation after charging with gas.

According to the invention there is provided a method of assembly a pneumatic piston and cylinder assembly which has a charging chamber adapted to be charged with gas under pressure and a piston member movable under the action of the pressure of the gas, the method including the steps of introducing a quantity of material in a liquid or paste form into the charging chamber, allowing said quantity to harden in situ and then charging the charging chamber with gas. Suitable materials may include wax, cold setting or heat setting synthetic resins or a water mixed cement mortar.

According to another aspect of the invention there is a provided a pneumatic piston and cylinder assembly which has been assembled according to said one aspect of the invention.

The invention will now be described by way of example with reference to the accompanying drawing which shows a longitudinal cross-section through one example of a pneumatic piston and cylinder assembly according to the invention.

Referring to the drawing, the pneumatic piston and cylinder assembly includes an outer cylinder 11, one end of which is closed by a guide housing 12 and the other end by an end plug 13. The end plug 13 is secured to the outer cylinder 11 by welding whereas the guide housing 12 is secured by setbolts 20 to a ring 30 which is welded to the outer cylinder 11. The guide housing 12 incorporates a through bore 14 in which is slidable a ramrod 15. An inner cylinder 16 spigots at one end into a counterbore 17 in the guide housing 12 where it is sealed by an 0 ring 18 so that it extends between the guide housing and the end plug 13 where it is located with a diametral clearance fit in a recess 19. The inner cylinder has castellations 21 at the end which is located in recess 19 and these, together with the diametral clearance fit, provide a restricted communication between the inside and outside of the inner cylinder 16 at the end where it is located in the end plug 13.

The through bore 14 in the guide housing 12 is interrupted by an annular sealing chamber 22 which encircles the ramrod 15.

This sealing chamber 22 communicates via a passage 23 with the interior of the inner cylinder 16. In use, the sealing chamber 22 is filled with oil which is separated from a charge of gas in a charging chamber 24 defined by the outer cylinder 11, the end plug 13 and the guide housing 12 by a separator piston 25. The separator piston 25 has a sealing ring 26 and a bearing ring 27.

To prevent the ramrod 15 sliding out of the guide housing 12, a head 28 is welded to the inner end. This head 28 is a sliding fit in the inner cylinder 16 and has a bearing ring 29 similar to bearing ring 27. The bearing rings 27 and 29 are of a plastics material and are slit axially or diagonally in the manner of piston rings. Hence oil from chamber 22 is not prevented from communicating with the separator piston 25 but the bearing ring 29 acts to restrict flow past the head 28.

The guide housing 12 has a pressure seal ring 31 to seal between the ramrod 15 and bore 14, this seal being wetted by oil in chamber 22 and thus remaining effective over a long period of service. A dirt scraper seal 32 protects the seal 31 from dirt and water, the presence of which is minimised by a bellows gaiter 33 which is clipped to the guide housing 12 and to a yoke 34 carried on the end of the ramrod 15.

The yoke 34 forms part of a linkage which transfers a thrust of the ramrod 15 extending from the guide housing 12 into a tensile force for tensioning a cable. This linkage forms no part of the present invention but a suitable linkage is described in British Patent Specification No. 1,137,081.

In use the ramrod 15 acts as a piston member, the thrust being created by virtue of the gas pressure from chamber 24 being transmitted through the diametral clearance and castellations 19 at the end of the inner cylinder 16 to the oil by means of the separator piston 25 so that the effective working diameter is that of the ramrod 15. If the cable under tension snaps, the ramrod is prevented from being driven by the high potential energy of the gas in chamber 24 by the restriction on gas flow given by the castellations 21 and by the restriction on oil flow given by the ramrod head 28. Furthermore, any large pressure drop between the charging chamber 24 and the interior of the inner cylinder 16 will tend to deform the inner cylinder 16 radially inwardly so as to grip the ramrod head 28 and the separator piston 25 and provide friction damping.

The annular sealing chamber 22 is provided with two tappings 35 and 36 which are used to inject a known quantity of oil into the chamber 22 and the interior of the cylinder 16 between the floating piston 25 and the ramrod 15. The charging chamber 24 is then charged with gas (e.g. nitrogen) through a third tapping 37 in the guide housing 12.

To obtain the correct relationship between thrust, ramrod extension and ambient temperature it is important to control the volume of gas in chamber 24 as well as the charging pressure. Known tensioners use a quantity of oil for this purpose but since this usually has the -disadvantage of absorbing some of the gas solid material is used. This is in the form of a wax which is added in molten form as a known volume which is allowed to solidify prior to pressurising the charging chamber 24 with gas.

One of the tappings 35 or 36 may be used for a pressure gauge so that form a check of pressure, ram extension and ambient temperature a service engineer can ascertain whether the cylinder assembly is operating correctly. Since the oil in chamber 22 is retained by the separator piston 25 the assembly can be used in any position without fear of oil draining from the chamber 22 so that the integrity of seal 31 is maintained.

Attention is hereby directed to co-pending Application No. 25777/77 (Serial No.

1601962) which claims other aspects of the piston and cylinder assembly just described.

WHAT WE CLAIM IS: 1. A method of assembling a pneumatic piston and cylinder assembly which has a charging chamber adapted to be charged with gas under pressure and a piston member movable under the action of the pressure of the gas, the method including the steps of introducing a quantity of material in liquid or paste form into the charging chamber, allowing said quantity to harden in situ and then charging the charging chamber with gas.

2. A pneumatic piston and cylinder assembly when assembled according to Claim 1.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (2)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   piston 25. The separator piston 25 has a sealing ring 26 and a bearing ring 27.

   To prevent the ramrod 15 sliding out of the guide housing 12, a head 28 is welded to the inner end. This head 28 is a sliding fit in the inner cylinder 16 and has a bearing ring 29 similar to bearing ring 27. The bearing rings 27 and 29 are of a plastics material and are slit axially or diagonally in the manner of piston rings. Hence oil from chamber 22 is not prevented from communicating with the separator piston 25 but the bearing ring 29 acts to restrict flow past the head 28.

   The guide housing 12 has a pressure seal ring 31 to seal between the ramrod 15 and bore 14, this seal being wetted by oil in chamber 22 and thus remaining effective over a long period of service. A dirt scraper seal 32 protects the seal 31 from dirt and water, the presence of which is minimised by a bellows gaiter 33 which is clipped to the guide housing 12 and to a yoke 34 carried on the end of the ramrod 15.

   The yoke 34 forms part of a linkage which transfers a thrust of the ramrod 15 extending from the guide housing 12 into a tensile force for tensioning a cable. This linkage forms no part of the present invention but a suitable linkage is described in British Patent Specification No. 1,137,081.

   In use the ramrod 15 acts as a piston member, the thrust being created by virtue of the gas pressure from chamber 24 being transmitted through the diametral clearance and castellations 19 at the end of the inner cylinder 16 to the oil by means of the separator piston 25 so that the effective working diameter is that of the ramrod 15. If the cable under tension snaps, the ramrod is prevented from being driven by the high potential energy of the gas in chamber 24 by the restriction on gas flow given by the castellations 21 and by the restriction on oil flow given by the ramrod head 28. Furthermore, any large pressure drop between the charging chamber 24 and the interior of the inner cylinder 16 will tend to deform the inner cylinder 16 radially inwardly so as to grip the ramrod head 28 and the separator piston 25 and provide friction damping.

   The annular sealing chamber 22 is provided with two tappings 35 and 36 which are used to inject a known quantity of oil into the chamber 22 and the interior of the cylinder 16 between the floating piston 25 and the ramrod 15. The charging chamber 24 is then charged with gas (e.g. nitrogen) through a third tapping 37 in the guide housing 12.

   To obtain the correct relationship between thrust, ramrod extension and ambient temperature it is important to control the volume of gas in chamber 24 as well as the charging pressure. Known tensioners use a quantity of oil for this purpose but since this usually has the -disadvantage of absorbing some of the gas solid material is used. This is in the form of a wax which is added in molten form as a known volume which is allowed to solidify prior to pressurising the charging chamber 24 with gas.

   One of the tappings 35 or 36 may be used for a pressure gauge so that form a check of pressure, ram extension and ambient temperature a service engineer can ascertain whether the cylinder assembly is operating correctly. Since the oil in chamber 22 is retained by the separator piston 25 the assembly can be used in any position without fear of oil draining from the chamber 22 so that the integrity of seal 31 is maintained.

   Attention is hereby directed to co-pending Application No. 25777/77 (Serial No.

   1601962) which claims other aspects of the piston and cylinder assembly just described.

   WHAT WE CLAIM IS: 1. A method of assembling a pneumatic piston and cylinder assembly which has a charging chamber adapted to be charged with gas under pressure and a piston member movable under the action of the pressure of the gas, the method including the steps of introducing a quantity of material in liquid or paste form into the charging chamber, allowing said quantity to harden in situ and then charging the charging chamber with gas.
2. 2. A pneumatic piston and cylinder assembly when assembled according to Claim 1.