GB2115550A - Improvements relating to housings for sensing elements - Google Patents

Abstract

A housing for a sensor for sensing a condition of a fluid in a duct 11 or container comprises a body part 13 for mounting in the wall of the duct or container and having a passage 16 extending along its length, an end cap 14 facing the inner end of the passage, and a tension spring 15 urging the end cap towards the body part. The sensor 18 is secured with its stem 19 extending along the passage 16 into abutment with the end cap 14 and the stem is of such length that the end cap is pushed away from the body part against the force of the spring 15 and breaks a seal between the end cap and body part about the inner end of the passage 16. The seal may be provided by the coils of the spring 15 itself which in such case is close- coiled and may have its coils coated with a resilient plastics material, or may be provided by a sealing ring disposed between the end cap and the body part. <IMAGE>

Description

SPECIFICATION Improvements relating to housings for sensing elements This invention relates to housings for sensing elements and is more particularly concerned with housings for sensing elements which it is desired to use for sensing a condition, for example the temperature, of a fluid in a duct or container.

It is usually necessary for such sensing elements to be removed occasionally for checking and/or replacement, and in many instances it is essential for the system which is being monitored or controlled to continue in uninterrupted operation whilst this is taking place. This requirement has led to the use of pockets which project into the duct or container and in which the sensing element can be disposed. Since the sensing element is thus out of direct contact with the fluid, the use of such a pocket in say a temperature control system inevitably results in delayed heat transfer between the fluid and the sensing element and hence in reduced sensitivity and accuracy of control, but allows the element to be withdrawn without the necessity to shut down the system.

According to this invention there is provided a housing for a sensing element for sensing a condition of a fluid in a duct or container, comprising a body part for mounting in the wall of the duct or container to project into the duct or container, which body part has a passage extending lengthwise thereof, an end cap facing the inner end of the passage, and spring means resiliently urging the end cap towards the body part, whereby insertion of the sensing element into the passage can move the end cap in a direction away from said inner end of the passage against the force of the spring means, the arrangement being such that when the sensing element is removed a seal is formed between the end cap and the body part preventing ingress of the fluid to the passage.

In a preferred arrangement a sealing ring is mounted on either the inner end of the body or the face of the end cap facing the inner end of the body so as when the sensing element is removed to form a seal between the body and the end cap which seal extends about the inner end of the passage.

In an alternative arrangement the seal is formed by the turns of a close-coiled tension spring sealingly connected to the body and the end cap and extending therebetween to constitute the spring means. The coils of the spring may be covered with a layer of a resilient material forming a seal between adjacent coils of the spring when the spring is in an unextended condition but leaving space between adjacent coils when the spring is extended.

Some embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows in axial section a temperature sensing installation incorporating a housing according to the invention, Figure 2 is a part-view corresponding to Figure 1 but illustrates the housing in its alternative condition, Figures 3 and 4 are respectively views corresponding to Figures 1 and 2 of an alternative construction of housing according to the invention, Figures 5 and 6 are respectively views corresponding to Figures 1 and 2 of another alternative construction of housing according to the invention, and Figure 7 is a sectional view on the line 7-7 of Figure 6.

Referring to Figures 1 and 2 of the drawings, the housing is secured in an internally threaded collar 10 welded to the periphery of an aperture in the wall 11 of a duct 12 along which flows a liquid whose temperature is to be monitored. The housing comprises an elongage body 1 3 which is in screw-threaded engagement with the collar at 1 Oa and projects into the duct, an end cap 14, and a close-coiled helical tension spring 1 5 opposite ends of which are in screw-threaded sealing engagement with the body 13 and the end cap 14. For this purpose the end portion of body 13 and the cap 14 are each formed with a screwthread of a cross-section appropriate to that of the wire material from which the spring is made.In its close-coiled condition illustrated in Figure 2, the coils of the spring close upon each other and form a seal preventing the liquid in the duct from leaking to any substantial extent into the space between the body 13 and the end cap. The elongate body 1 3 has a recess 1 5 in its upper end and a central passage 1 6 extends from the recess and opens to the end face of the body opposite the end cap. The terminal block 18 of a thermocouple or platinum resistance thermometer is secured in the recess in the housing and has a sensorcontaining stem 1 9 extending down the passage 1 6 and abutting the bottom of a shallow locating recess 20 in the end cap.The length of the stem is greater than the distance between the base 21 of recess 1 5 and the bottom of recess 20, so that as the securing screws 22 of the block 18 are tightened, the block is pushed downward and the bottom end of the stem pushes the end cap 14 away from the elongate body and opens the coils of the spring as shown in Figure 1, allowing the liquid to flow about the sensor at the lower end of the stem. Leakage of the liquid up the central passage 1 6 is prevented by a sealing ring 23 which is disposed in a groove in the passage 1 6 and which engayes the stem. Leakage along the screw-thread in the collar 10 is prevented by a sealing ring 24 disposed between the top of the collar 10 and the underside of the enlarged head at the outer end of the body 13.

Conversely, as the securing screws 22 are removed and the block 1 8 is withdrawn the spring 1 5 contracts to its close-coiled condition and re-forms the seal against ingress of the liquid into the space within the spring.

Thus, the arrangement gives the advantage of direct contact between the liquid and the sensing element whilst permitting the element to be removed, for exchanging or checking, without the need to close down the liquid flow system. In one such arrangement, there is a force of 20 to 30 Ibs between adjacent coils of the spring when the spring is fully contracted.

If desired, in order to obtain a tigher seal, the material of the spring may be coated with a resilient plastics material.

In a preferred arrangement illustrated in Figures 3 and 4, in which the parts not illustrated are the same as in the arrangement of Figures 1 and 2, the tension spring 15a does not itself provide the seal when the block 1 8 is removed but instead draws the end cap 14 into sealing abutment with the inner face of the body 1 3 through a sealing ring 26 extending about the end of the passage 16.

The sealing ring 26 may be in the form of a flat washer as shown or in the form of an O-ring retained in an annular groove in the end face of the body.

The tension spring 15a is an open-coiled spring in this arrangement and although opposite ends of the spring are secured to the body and end cap by being screw-threaded thereon, the ends of the springs are not sealed with respect to the body and end cap and the inner end portion of the body is reduced in diameter to increase the length of the part of the spring which is free to move.

Insertion of the block 18 pushes the end cap away from the body against the force of the spring, breaking the seal and allowing the fluid into direct contact with the sensing element.

Various other arrangements are possible. For example, the end cap may have a skirt extending upward about and in axial sliding engagement with the lower end portion of the body, the skirt having openings therein which are blanked off and sealed by the body when the sensor is removed and the spring draws the end cap upward but which are opened when the sensor is placed in position and pushes the end cap downward.

Figures 5 to 7 show another alternative arrangement in which the end cap 30 has a skirt 31 extending upward about and in axial sliding engagement with the lower end portion of the body. Two axially spaced rings of radial ports 32, 33 extend through the skirt. The upper end portion 34 of the skirt has the lower end of a tension spring 35 connected to it in the same way as to the cap in the previously described constructions.

Two axially spaced rings of radial ports 36, 37 extend also through the lower end portion of the body. When the sensor 19 is inserted, the end cap 30 is pressed down against the spring force and the ports 32, 33 in the skirt come into register with the ports 37 and the space 38 within the cap and immediately adjacent the end of the body, while the ports 36 in the body are uncovered by the downward movement of the upper end portion 34 of the skirt, so that fluid can circulate directly about the lower end portions of the sensor. When the sensor is withdrawn, the ports in the skirt are sealed by the body and the ports in the body are sealed by the skirt of the end cap.

Claims (7)

1. A housing for a sensing element for sensing a condition of a fluid in a duct or container, comprising a body part for mounting in the wall of the duct or container to project into the duct or container, which body part has a passage extending lengthwise thereof, an end cap facing the inner end of the passage, and spring,means resiliently urging the end cap towards the body part, whereby insertion of the sensing element into the passage can move the end cap in a direction away from said inner end of the passage against the force of the spring means, the arrangement being such that when the sensing element is removed a seal is formed between the end cap and the body part preventing ingress of the fluid to the passage.

2. A housing as claimed in claim 1 wherein a sealing ring is mounted on either the inner end of the body or the face of the end cap facing the inner end of the body so as when the sensing element is removed to form a seal between the body and the end cap which seal extends about the inner end of the passage.

3. A housing as claimed in claim 1, wherein the seal is formed by the turns of a close-coiled tension spring sealingly connected to the body and the end cap and extending therebetween to constitute the spring means.

4. A housing as claimed in claim 3, wherein the coils of the spring are covered with a layer of a resilient material forming a seal between adjacent coils of the spring when the spring is in an unextended condition but leaving spaces between adjacent coils when the spring is extended.

5. A housing as claimed in claim 1, wherein the end cap has a skirt portion in telescoping sealing engagement with the body, the skirt and/or the body having porting therein which is closed off when the sensing element is removed but which is opened to admit fluid to the space between the body and the end cap when the sensor is inserted into the passage.

6. A housing substantially as hereinbefore described with reference to and as illustrated in Figures 1 and 2 or Figures 3 and 4 of the accompanying drawings.

7. The combination with a housing as claimed in any one of claims 1 to 6 of a sensing element having a portion which extends along said passage in the body part into abutment with the end cap, the sensing element being in sealing abutting engagement with the body in a direction axially of the passage and said portion thereof having a length such that the seal between the end cap and the body is broken.