GB2204366A - Mechanical seal testing system - Google Patents

Abstract

A mechanical seal arrangement including a primary mechanical seal 11 and a secondary mechanical seal 12 and a system for checking the status or condition of the secondary mechanical seal. The system comprises a rotary switch valve 23 to which is connected an alarm activating pressure fluid supply 13, 14, a product leakage line 28 and an exhaust outlet 27, the product leakage line being used when checking the status or condition of the secondary mechanical seal 12, i.e. it is the part of the aforesaid pressure line which is primed with fluid pressure from the activating alarm pressure fluid supply and which is isolated from the latter by the rotary switch valve to permit the status of condition of the secondary mechanical seal to be determined by any pressure drop thus indicating whether or not there is deterioration of the secondary mechanical seal. <IMAGE>

Description

MECHANICAL SEALS This invention relates to mechanical seals.

It is well known to provide a mechanical seal arrangement consisting of a primary mechanical seal and a secondary mechanical seal, the latter coming into action on failure of the primary mechanical seal.

It is highly desirable that a warning be given upon primary mechanical seal failure, especially but not exclusively when the mechanical seal arrangement is being used tc seal dargerous fluid products such as poisonous and/or flammable fluid products. The operator of the system incorporating the mechanical seal arrangement will then be aware that the sealing of the system is dependent upon the secondary mechanical seal and will then be in a position to take immediate or timely action to replace the failed primary mechanical seal.

It will be manifest that if a mechanical seal arrangement as aforesaid has been operational for some considerable time then there might be deterioration of the secondary seal and consequently there is a risk of total seal failure, i.e. failure of both the primary and secondary mechanical seals simultaneously or successively in a period of time inadequate to permit replacement of the failed primary mechanical seal, and consequently it is an object of the present invention to provide a mechanical seal arrangement comprising a primary mechanical seal and a secondary mechanical seal and having operatively connected thereto a system for checking the status or condition of the secondary mechanical seal.

As aforesaid such mechanical seal arrangements are often used to seal product lines through which dangerous fluid products are conveyed ano i is another object of the present invention to provide, combined with the mechanical seal arrangement, a secondary mechanical seal status or condition checking system which is purely pressure activated and which does not employ any electrical or battery power so that the checking system is intrinsically safe. This is particularly desirable when the fluid product is flammable.

Where the expression "mechanical seal arrangement" is used hereinafter it is to be understood that this means an arrangement including a primary mechanical seal and a secondary mechanical seal.

According to the present invention there is provided a mechanical seal arrangement comprising a primary mechanical seal, a secondary mechanical seal and a system for checking the status or condition of the secondary mechanical seal, the system comprising a supply of pressure fluid connected via a pressure line to the mechanical seal arrangement, a normally closed valve in the pressure line adapted to isolate the pressure fluid from the mechanical seal arrangement and openable to permit flow of pressure fluid to the mechanical seal arrangement for status or condition check purposes, the pressure line also incorporating a pressure gauge.

Preferably the normally closed valve means is operable to isolate part of the pressure line primed with pressure fluid from the supply of pressure fluid whereby any pressure drop due to decay of the secondary mechanical seal can be detected by an inspection of the pressure gauge.

Preferably the normally closed valve means is operable to connect the primed part of the pressure line connected to the mechanical seal arrangement to an exhaust outlet.

Preferably the normally closed valve means is a rotary switch valve to which is connected an activating pressure fluid supply of an alarm means, the product leakage line and the exhaust outlet, the product leakage line being used when checking the status or condition of the secondary mechanical seal, i.e. it is the part of the aforesaid pressure line which is primed with fluid pressure from the activating alarm pressure fluid supply and which is isolated from the latter by the rotary switch valvc to permit the status of condition of the secondary mechanical seal to be determined by any pressure drop thus indicating whether or not there is decay of the secondary mechanical seal.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which Fig. 1 is a fluid pressure circuit diagram of a combined primary mechanical seal failure warning system and secondary mechanical seal status checking system, the circuit being in the normal standby mode condition; Fig. 2 is a view of the circuit indicating the condition of the circuit when there is a pressure leak from the primary mechanical seal; Fig. 3 is a view of the circuit indicating the condition of the circuit with the leaking product being exhausted to atmosphere with flaming of the product if necessary; Fig. 4 is a view of the circuit showing the condition of the circuit when the status or condition of the secondary mechanical seal is being checked; Fig. 5 is a view of the circuit showing the condition of the circuit whe;;! tescin the status, i.e. degree of deterioration, if any, of the secondary mechanical seal; and Fig. 6 is a view of the circuit showing the condition of the circuit when the fluid pressure is being exhausted after testing of the secondary mechanical seal.

The mechanical seal arrangement is indicated at 10 and comprises a primary mechanical seal 11 and a secondary mechanical seal 12. In this case the secondary mechanical seal lz is a dry running contact seal but the present invent c is nct restricted to such secondary mechanical seals.

The circuit is provided with a supply of activating pressure fluid which is preferably either a factory air supply 13 or CO2 normally provided from a reservoir 14. Both of these supplies may be provided with the CO2 supply swerving as a backup should the main air supply fail for whatever reason.

The supply of activating pressure fluid 13 or 14 is delivered into the warning and checking system via a stop valve 15 and a pressure regulator 16 with associated pressure gauge 17.

The elements of the system which warn of a leakage from the primary mechanical seal 11 comprise a visual indicator 18 in the form of a pressure lamp as previously mentioned and an audible alarm 19 (whistle or siren). A normally closed pilot operated control valve 20 is disposed upstream of the warning elements 18 and 19 and in the standby condition of Fig. 1 serves to isolate these warning elements 18 and 19 from the activating pressure fluid supply.

Between the pressure lamp 18 and the audible alarm 19 is a key operated normally open control valve 21. This valve can be used to isolate the audible alarm 19 from the warning system 0! te shunt off the audible alarm once the warning system has been activated and the failure of the primary secondary seal 11 noted by operatives.

The combined warning and checking system incorporates downstream of the control valve 20 a second visual indicator 22 again in the form of a pressure lamp. The purpose of this indicator 22 is to show that the system is primed with activating pressure fluid.

The warning visual indicator 18 is iDreferably coloured red while the primed visual indicator 22 is preferably coloured green. Other colours may be employed provided the two indicators are of different colours.

The system further includes a four-position rotary switch valve 23 which is normally closed.

The rotary switch valve is connected to the activating pressure fluid supply 13 or 14 via a pressure line 24 incorporating a pressure regulator 25 and a non-return valve 26.

The rotary switch valve 23 is also connected to an exhaust outlet 27 through which either activating pressure fluid or product can be exhausted.

Finally, the rotary switch valve is connected to the mechanical seal arrangement by a product line 28 which incorporates a pressure gauge 29 and from which there is a branch line 30 to the pilot of the pilot operated control valve 20.

In Fig. 1 it can be seen that the circuit of the combined warning and checking system is primed with activating air or CO2. In this normal standby mode condition the visual indicator 22 has been operated to indicate the priming condition and the circuit is filled with air or CO2 as far as the control valve 20 and the rotary switch valve 23 which isolates thc air or C02 supply from the product line 28 and the exhaust outlet 27, the control valve 20 isolating the warning visual indicator 18 and the audible alarm 19 from the air or CO2 supply.

The condition of the circuit which occurs when there is failure of the primary mechanical seal 11 or a leakage therefrom is shown in Fig. 2 and here it will be seen that product flowing along pressure line 28 operates the pressure gauge 29 and also via the branch line 30 operates the pilot operated control valve 20 to open same and allow activating air or COi to operate the warning visual indicator 18 and via the control valve 21 the audible alarm 19.

When the failure or leakage from the primary mechanical seal 11 has been noted the audible alarm 19 can be shut off by means of the key operated control valve 21.

The mechanical seal arrangement is now running on the secondary mechanical seal 12 and operatives can thus take action to replace the failed or damaged primary mechanical seal 11.

Fig. 3 shows the condition of the circuit in which action has been taken to exhaust product from the product line 28 through the exhaust outlet 27.

This is effected by operating the rotary switch valve 23 to connect the pressure line 28 to the exhaust outlet 27. It will be noted that in this condition the audible alarm 19 is normally rendered inoperative by the control valve 21.

When it is desired to check the status or condition of the secondary mechanical seal 12, which can be done at regular intervals or whenever is appropriate, the rotary switch valve 23 is operated to connect the activating air or C02 supply 13 or 14 te the product pressure line 28 tnereby pressulising the secondary mechanical seal 12. This also serves to operate the warning visual indicator 18 and, if in circuit, the audible alarm 19 due to activating air or CO2 passing along branch line 3u to open the pilot operated control valve 20.

By operating the rotary switch valve to isolate the pressurised product line 28 from the activating air or CO2 supply 13 or 14 the status or condition of the secondary mechanical seal 12 can be determined by any pressure drop which wnll be shown or. the pressure gauge 29 (see Fig. 5).

To clear the product line 28 of pressurised air or CO2 the rotary switch valve 23 is operated to connect the pressure line 28 to the exhaust outlet 27 and this permits the pilot operated control valve to close (see Fig. 6).

The combined warning and testing system of the present invention can be applied to multiple mechanical seal arrangements and a selected mechanical seal arrangement can be tested at will.

It will be manifest that appropriate valving will be provided in such a multiple mechanical seal situation.

It is to be noted that the rotary switch valve 23 is keyed to restrict unauthorised use.

Claims (4)

CLAIMS:-

1. A mechanical seal arrangement comprising a switch valve in the normal standby mode condition of primary mechanical seal, a secondary mechanical seal, and a system for checking the status or condition of the secondary mechanical seal, the system comprising a supply of pressure fluid connected via a pressure line to the mechanical seal arrangement, and a normally closed valve in the pressure line adapted to isolate the pressure fluid from the mechanical seal errangement and openable to perrit flow of prcssure fluid to the mechanical seal arrangement for status or condition check purposes, the pressure line also incorporating a pressure gauge.

2. A mechanical seal arrangement as claimed in claim 1, in which the normally closed valve means is operable to isolate part of the pressure line primed with pressure fluid from the supply of pressure fluid whereby any pressure drop due to decay of the secondary mechanical seal can be detected by an inspection of the pressure gauge.

3. A mechanical seal arrangement as claimed in claim 1 or 2, in which the normally closed valve means is operable to connect the primed part of the pressure line connected to the mechanical seal arrangement to an exhaust outlet.

4. A mechanical seal arrangement as claimed in any one of claims 1 to 3 in which the normally closed valve means is a rotary switch valve to which is connected an activating pressure fluid supply for alarm means, the product leakage line and the exhaust outlet, the product leakage line being used when checking the status or condition of the secondary mechanical seal, i.e. it is the part of the aforesaid pressure line which is primed with fluid pressure from the activating alarm pressure fluid supply and which is isolated from the latter by the rotary switch valve to permit the status or condition of the secondary mechanical seal to be determined by any pressure drop thus indicating whether or not there is deterioration of the secondary mechanical seal.