GB2528836A

GB2528836A - Mechanical seal control mechanism

Info

Publication number: GB2528836A
Application number: GB1411427.6A
Authority: GB
Inventors: Carl-Eiler Rodgrigues
Original assignee: AES Engineering Ltd
Current assignee: AES Engineering Ltd
Priority date: 2014-06-26
Filing date: 2014-06-26
Publication date: 2016-02-10
Anticipated expiration: 2034-06-26
Also published as: GB2528836B; GB201411427D0; US20150377359A1

Abstract

A mechanical seal control mechanism is provided. The mechanical seal comprises: one or more seal faces under axial contact through a spring biasing means (12 in Figure 1); a longitudinally floating first member (7 in Figure 1); a longitudinally non-floating member (3 in Figure 1); a longitudinally floating seal face (9 in Figure 1); an a longitudinally non-floating second seal face (10 in Figure 1). The seal includes a thermally responsive element 14, which reduces or negates face contact pressure at the sealing interface 13 when heat is generated within the seal above a predetermined temperature. The thermally responsive element may take the form of a bimetal 14 or a shape memory alloy spring (17 in Figure 6).

Description

MECHANICAL SEAL CONTROL MECHANISM

Field of the Invention

The present invention relates to a mechanical seal control mechanism and particularly to the use of a smart material with the ability to convert temperature S change into a reduction in face contact pressure within a mechanical seal in the undesired operating condition commonly referred to as dry running".

Background to the Invention

A mechanical seal generally comprises a rotating member attached to the pump shaft and a stationary member attached to the pump housing. The rotating member is in relative contact with the stationary member, which provides the seal. Both the rotating member and the stationary member are commonly referred to in the mechanical sealing industry as seal faces'. A basic operating principle of mechanical seals is that the seal faces require a fluid film' that provides a lubricant between them in order to function correctly.

The operating condition of dry running" occurs between the seal faces when a fluid film' is not present to lubricate them. This results in the faces being in direct contact while in operation and thus generating heat. This heat can cause the faces to wear and the contacting elastomers to distort and melt, in turn causing the mechanical seal to fail.

Reducing face contact pressure or friction between the rotary and stationary faces during periods of dry running can reduce heat generation, face wear and elastomer damage.

Current solutions include; Polycrystalline Diamond Coatings adhered to the faces with the aim to reduce face contact wear by increasing hardness.

Amorphous Diamond-Like Coatings adhered to the faces with the aim to reduce face temperature through decreased friction.

Dual seals providing a "stable" lubrication from a dedicated system, and do not rely on the process fluid, however they can still falter through the system fluid finishing or the system being inadvertently shut off.

Problems still exist with these solutions including; cost, reliability and application limitations.

Statements of the Invention

The present invention relates to a device whereby the face contact pressure caused by the spring pressure is negated by the force produced when the thermally activated Smart Material shape is altered.

The aforementioned "Smart Material" may comprise a Bimetal, Shape Memory Alloy (for example Nitinol) or Shape Memory Polymer. Additionally, the smart material may comprise a combination of one or more those items. A "smart material" is intended to be a shape-memory material that is sensitive to thermal changes such that it increases or decreases in size and/or shape when subjected to a change in temperature. Preferably, the change is a two-way change, although it may be desirable to employ a one-way shape-change material in certain circumstances. The advantage of a two-way change is that where the material has changed shape upon heating to reduce the face contact pressure, upon the system cooling, the pressure can be increased to retain the integrity of the seal.

A problem is addressed by distinguishing the condition of dry running from normal operating conditions and implementing a mechanical system able to reduce or eliminate face pressure through separation of the faces. An advantage of using a smart material to address this problem is that it can be incorporated into an element of the seal mechanism and so have a direct effect on the seal faces. Additionally, it may be possible to retrofit such parts into existing seal mechanisms.

Additionally, when utilising a bimetal or shape memory alloy it can be used within seals operating at differing temperatures by specifying the material to alter shape at the appropriate temperature. This provides an advantage in that the system can be operated at predetermined temperatures to provide a predetermined thermal response.

Brief Description of the Drawings

The accompanying drawings are as follows:-Figure 1 shows a cross sectional side view profile of a typical mechanical seal Figure 2 shows an enlarged cross sectional side view profile of a typical mechanical seal in operational conditions using the first embodiment of a bimetal Figure 3 shows an enlarged cross sectional side view profile of a typical mechanical seal in dry running conditions using the first embodiment of a bimetal Figure 4 shows an enlarged cross sectional side view profile of a typical mechanical seal in operational conditions using the second embodiment of a bimetal Figure 5 shows an enlarged cross sectional side view profile of a typical mechanical seal in dry running conditions using the second embodiment of a bimetal Figure 6 shows an enlarged cross sectional side view profile of a typical mechanical seal in operational conditions using an SMA Spring Figure 7 shows an enlarged cross sectional side view profile of a typical mechanical seal in dry running conditions using an SMA Spring

Detailed Description of the Drawings

The invention will now be described by way of examples only, with reference to the accompanying drawings.

Figure 1 shows a cross sectional side view profile of a typical mechanical seal 1, that comprises of a pump housing 2, a longitudinally non floating member the gland 3 which is fixed to said pump housing, the atmosphere 4, a shaft 5 which axially aligns with the said gland, a process fluid 6 contained within the said pump housing, a longitudinally floating second member the shaft sleeve 7 which attaches axially to the said shaft, an elastomeric sealing member a rotary 0-ring 8, a longitudinally floating seal face the rotary 9, a longitudinally non floating seal face the stationary 10, a secondary elastomeric sealing member a stationary 0-ring 11, and a spring biasing means 12.

In operation, the stationary floating seal face 10 is energized by the spring 12 causing the seal face 9 to contact said stationary seal face 10. Between said seal faces 9 and 10 a fluid film of lubrication is provided by the process fluid being pumped 6.

Figure 2 shows an enlarged cross sectional side view profile of a typical mechanical seal in operational conditions with fluid 6, present between the faces 13. It shows the first embodiment using a bimetal 14, and circlip 15 in normal operational conditions.

Figure 3 shows an enlarged cross sectional side view profile of a typical mechanical seal in dry running conditions with no fluid 6, present between the faces 13, causing initial direct contact. It shows the first embodiment using a bimetal 14, and circlip 15 to fit said bimetal. In this condition a reduction in pressure between the seal faces is obtained by negating the spring biasing means through deflection of the disc acting on the stationary seal face, moving the faces away from each other. When faces reach a predetermined temperature, the bimetal deflects. When the faces return to predetermined temperature the bimetal returns to their original shape.

Figure 4 shows an enlarged cross sectional side view profile of a typical mechanical seal in operational conditions with fluid 6, present between the faces 13. It shows the second embodiment of a bimetal 15, altering the location within the seal, acting directly on the face forcing a gap between them.

Figure 5 shows an enlarged cross sectional side view profile of a typical mechanical seal in dry running conditions with no fluid 6, present between the faces 13, causing initial direct contact. It shows the second embodiment of a bimetal 15, the alternative location offers a faster response to temperature changes.

Figure 6 shows an enlarged cross sectional side view profile of a typical mechanical seal in operational conditions with fluid 4. It shows the third embodiment of a Smart Memory Alloy Spring 17 in normal operational conditions.

Figure 7 shows an enlarged cross sectional side view profile of a typical mechanical seal in dry running conditions with no fluid 6, present between the faces 16, causing initial direct contact. It shows the third embodiment of a Smart Memory Alloy Spring 17 in dry running operation conditions where heat is present. A reduction in face pressure is initiated through the heat transfer to the back face and into the spring 17.

On heating the spring contracts, opening the faces 16 and when temperature is normalised the spring extends to normal working lengths. :io

Claims

Claims 1. A mechanical seal comprising of one or more seal faces under axial contact through a spring biasing means, a longitudinally floating first member, a longitudinally non-floating member, a longitudinally floating seal face, a longitudinally non-floating second seal face, and comprises a thermally responsive element, which reduces or negates face contact pressure when heat is generated within the seal above a predetermined temperature threshold.
2. A device according to claim 1, wherein the said element comprises a Smart Material.
3. A device according to claim 1 or claim 2, wherein the temperature threshold correlates with the maximum operating temperature of the contacting elastomers.
4. A device according to any one of claims 1 to 3, wherein the heat is generated through contact between said floating seal face and said second non-floating seal face and that heat is linked to the thermally responsive element.
5. A device according to any preceding claim, where the thermal response is predetermined to suit the application and, when in use, the thermal response alters the pressure on the one or more seal faces.
6. A device according to claim 4, wherein heat is generated as a result of direct face contact on the one or more seal faces without lubrication.
7. A device according to claim 6, wherein, when in use, the heat generated is as a result of misalignment of the one or more seal faces.
8. A device according to any preceding claim, wherein the face contact is caused through a loss in chamber pressure.
9. A device according to any preceding claim, wherein the device comprises one or more elements from a group comprising: a spring; disc; wire; sheet; or ring.