GB2170353A - Seal for a fluid-operable device - Google Patents

Abstract

A seal, for use in a fluid-operable device, or a part thereof is made of a material incorporating a constituent which is capable of magnetic polarisation, thereby to enable the seal or the part thereof to be magnetised, whereby, on relative movement between an element 4 of the device on which the seal 7 is mounted and a magnetically operable switch 8, operation of the switch 8 will be effected. The material may be barium ferrite. The seal 7 may be formed with a body portion and a more-flexible lip or sealing portion 10, each of an elastomeric material of which only the elastomeric material of the body portion incorporates the magnetically polarizable constituent. <IMAGE>

Description

SPECIFICATION Seal for a fluid-operable device The invention relates to a seal for use in a fluid-operable device ofthe kind including a movable element to be subjected on operation to a pressure difference atopposed ends or sides ofthe element.

Such an element may be a piston or a diaphragm movable in a housing and used to transmit power or a valve member or valve actuator, the element having a peripheral seal acting between the element and the housing.

In such applications it may be necessary to sense the position ofthe element in the housing in order to effect sequential operation of the element. This may be performed by one or more magnetically-operable switches arranged ot be actuated when the element reaches one or each of a plurality of predetermined positions, for example the ends ofthe stroke of a piston, thus giving an electrical signal, or series of electrical signals, to effect the sequential operation of the element. For example, where the element is a piston movable in a cylinder, the piston may carry a permanent magnet or magnets movable past a stationary magnetically-operable switch or switches mounted externally of the interior ofthe cylinder. The incorporation of a magnet in the piston may present problems and thus increase production costs.For example, it is sometimes difficult to fined space to accommodate the magnet in a piston and so it may be necessary to design and manufacture a special piston.

If a unitary magnet is used, the piston, or other movable element, may have to be constructed in two parts to permitthe magnetto be mounted therein.

In accordance with the invention, a seal for use in a fluid-operable device is made from an elastomeric material incorporating a constituentwhich is capable of magnetic-polarization, thereby to enable the seal or a partthereofto be magnetized, whereby, on relative movement between an element of the device on which the seal is mounted and magnetically-operable switch means, operation of the switch means will be effected.

By magnetic-polarization of the constituent which is incorporated in the seal or said part thereof, the seal or said part thereof becomes magnetized and so in a fluid-operable device including the seal, according to this invention,the aforesaid disadvantages are avoided.

The magnetically-polarizable constituent may be ferrite, for example barium ferrite.

The magnetically-polarizable constituent is conveniently dispersed in the elastomeric material.

The seal may comprise a body portion and a more-flexible lip or sealing portion, each said portion being made of an elastomeric material of which only the elastomeric material of the body portion incorporates the magnetically-polarizable constituent.

The invention also includes a fluid-operable device having a movable element provided with a seal as set out hereinbefore.

Byway of example, several embodiments of a fluid-operabie device having a movable element provided with a magnetic seal, in accordance with the invention, are now described with referencetothe accompanying drawings, in which: Figures 1-3 are axial sectionsthrough three different piston and cylinder devices in each of which the piston is provided with a seal or seals in accordance with the invention, and Figure 4 is an axial section through a piston valve in which the piston is provided with a seal in accordance with this invention.

Referring to Figures 1-3, each device comprises a piston rod 1 which is movable in a cylinder2 in known manner. In each case, the piston rod 1 carries at its inner end a piston 3 or 4 provided with at least one annularmagneticseal 5, 60r7in accordancewiththe invention. In Figure 1,theseal 5 is bonded to the piston 3which is a non-ferrous plate bolted or otherwise attached to the piston rod 1. In Figure 2, a pair of seals 6 each having an annularflexible sealing lip 9 extending in a direction axially-outwardlythereof are fitted in peripheral grooves in the piston 4which is of non-ferrous material and which is mounted on a screw-threaded end ofthe piston rod 1 or otherwise secured thereto. In Figure 3 the seal 7 is of a double-acting kind mounted in a peripheral groove in the piston.The seal 7 has a pair of flexible annular sealing lips 10 extending in opposite axial directions thereof. Each of the seals 5, 6 or 7, is moulded from an elastomeric material in which a magnetically-polarized material is dispersed in or is moulded in the material. The magnetically-polarizable material may, for example, be barium ferrite or anotherferrite. In the case of the seal 6 or7, the respective flexible lips 9 or 10 do not contain the magnetically-polarizable material, this being in the central body part of the seal only.

Before use, each of the seals, orthe body partsthereof, are polarized magnetically, that is they are magnetized, and soon movement ofthe piston within the cylinder, a magnetically-operable switch or switches mounted on the outside of the cylinder 2 atafixed position or positions will be operated by the passage of the piston. In this way, sequential operation of the device is effected or an indication of when the piston has reached a certain position or positions is obtained.

In Figures 1-3, only one magnetically-operable switch 8 atthe position ofthe inner end of the stroke ofthe piston is shown. A plurality of such switches, each located at different positions in the stroke of the piston may alternatively be provided.

InFigures2and3,thelips9and10remain unpolarized and are therefore moreflexiblethan the polarized body portions ofthe respective seals. The lip and body portions ofthe seals 6 and 7 may be moulded in two different elastomeric materials, one more flexible than the other. In this way the seal can be given optimum wear properties and flexibility atthe sealing surfaces.

In Figures 1-3 normal, non-magnetic, O-ring seals 11 are also shown.

Referring to Figure 4, the piston valve comprises a ported housing 12 containing a piston valve member 13 fitted with sealing O-rings 14. O-ring seals 15 are also shown atthe ends of the housing. The O-ring seals 14 and 15 are of a normal non-magnetic kind. In accordance with the invention, the valve member 13 is fitted with a magnetizable O-ring seal 16 at one or more positions. The O-ring seal 16 slides sealingly within the housing 12 and is moulded from an elastomeric material which hasa magnetically-polar izable materiatdispersedtherein,forexample barium ferrite. Before use, the seal 16 is polarized and thus becomes magnetized. As in the devices of Figures 1-3, at least one magnetically-operatedswitch 8 is mounted outside the housing 12 and is operated by the or each seal 16 when it reaches the position ofthe switch 8. In this way the sequential operation ofthe valve is effected or an indication ofthe instantaneous position ofthe valve member is obtained.

In the examples illustrated, the seals 5,6,7 and 16 are used asthe magnets foroperating the switch or switches 8 and so no separately constructed magnet has to be mouned on the piston or valve member.

Thus a cheaper and more compact assemblu is obtained.

Claims (7)

1. A seal for use in a fluid-operable device, the seal ora partthereofbeing madeof a material incorporating a constituentwhich is capable of magnetic polarization, therebyto enable the seal ora part thereofto be magnetised, whereby, on relative movement between an element of the device on which the seal is mounted and magnetically-operable switch means, operation ofthe switch meanswill be effected.

2. The seal as claimed in Claim 1 inwhichthe magnetically-polarizable constituent is a ferrite.

3. The seal as claimed in Claim 2 in which the ferrite is barium ferrite.

4. The seal as claimed in any preceding claim in which the magnetically-polarizable constituent is dispersed in the elastomeric material.

5. The seal as claimed in any preceding claim comprising a body portion and a more-flexible lip or sealing portion, each said portion being made of an elastomeric material of which onlythe elastomeric material ofthe body portion incorporates the magnetically-polarizable constituent.

6. Afluid-operable device having a movable element provided with a seal according to any one of Claims 1-5.

7. Afluid-operable device, or seal therefor, constructed and arranged substantially as described herein and shown in any one of Figures 1 to 4 ofthe drawings.