WO1997044645A2

WO1997044645A2 - Device for testing safety valves

Info

Publication number: WO1997044645A2
Application number: PCT/SI1997/000018
Authority: WO
Inventors: Boz^¿o LEGAT; Peter S^¿KOFIC
Original assignee: L-Plan, Podjetje Za Projektiranje, Meritve In Prodajo, D.O.O.
Priority date: 1996-05-21
Filing date: 1997-05-20
Publication date: 1997-11-27
Also published as: AU3053997A; WO1997044645A3; SI9600167A

Abstract

This invention relates to device for testing and depicting characteristics of the safety valves during or out of the working of pressure system or pressure device. Device for testing safety valves according to invention comprises driving complex (31) with working complex (32), bearing complex (33) for mounting device on safety valve (34), pressure transducer (18) and electronic unit (15), taking in consideration that driving complex (31) comprises electromotor (1) with optoelectronic giver, reductor (2), snail (3), snail gearing (4) with inner thread and that in it is moving screw (6) with clamping head (7) and that in particular embodiment between moving screw (6) and clamping head (7) is placed measurer of the force (36). Device for testing safety valves based on invention is mounted on tested safety valve and via driving lifts spindle (12) of valve (34) and measuring and analyzing lift of spindle (12), lifting force and pressure in the system.

Description

Dβvice for testing safety valves

This invention relates to device for testing and depicting the characteristics of the safety valves during or out of the normal working process of the pressure system or pressure device.

The problem solved by the present invention is such construction of the device for testing safety valves, that is small in dimensions and that allows easy to carry or transport via the energetic installation to the hardly approachable places and at the same time allows simple to work with, essentially shortens the time between the mounting, start of the test and end of the test.

Safety valves are designed for prevention of rising pressure in system over the allowable limit. This limit can be defined - fixed with the help of the mechanism and calibrated spring, which allows the opening of the valve at the set pressure. When the pressure in the system - force, that is acting on the disc, spindle and spring, reaches the force of the spring • which is acting in the opposite direction, the safety valve commence to open (set pressure or the opening pressure). Different shapes of the discs are allowing different lifts and flows, that are necessary, that from the system is released more medium, than it is lead in the system or the system is capable of producing it. Maximal lift or move of the disc it's called maximum opening pressure. When releasing the system, the pressure in it is dropping, the force acting on the disc is decreasing and when it is leveled with the force of the spring, the spindle with spring and disc returns to it's original position in the way that assures tightness (closing pressure of the valve).

In practice this kind of tests are performed by successive raising of the pressure inside the pressure devices or pressure vessels, where valves need to be tested, until we reach in advance settled pressure. This procedure includes great difficulties because normal activities are interrupted. Devices or vessels must be loaded with the pressure which is essentially higher then the normal working pressure, which causes substantial tensions in the material. Also considerable additional energy must be put in raising pressure in the system. Industrial devices and systems often include several safety valves, each valve is set in dependance of the technical requests. In this way all the safety valves, which have lover opening pressure than the testing pressure, must be corked, which causes a lot of additional work and problems through all the procedure.

Another way for testing the safety valves is on the test rig, which is very accurate, but can be performed only when system is shut down, so that the safety valves can be dismounted. This sometimes can't be done because of the big dimensions or some other reasons and at the same time it takes a lot of time. With this testing, called also cold testing, it is impossible to consider working conditions, mostly the temperature during the normal production.

Up to the present, there are two devices known for the testing of the safety valves:

TREVITEST manufactured by Furmanite, described in the patent EP 0 028 661 B1 , which overcame the force with the hydraulic system and cylinder. Compressor fills compressed air in the multiplicator, which with the differences in the area of the pistons raises pressure in the oil. This overcame the height to the hydraulic cylinder which is mounted on the construction of the device, which is mounted on the safety valve. In this cylinder pressure is once more multiplied, which generates enough big force to overcame the force of the spring of the safety valve, pressure in the system where safety valve is mounted and lift of the spindle of the safety valve. Solution is unpractical because of the size of the additional devices with which we reach the pressure, ei. compressor and multiplicator, which unable the persons to deal with the transportation and mounting on to the hardly accessible places in the energetic stations and installations, as close as possible to the safety valve. Also the hydraulic cylinder on the construction raises it's height, so that in many cases isn't possible to test the safety valves, which don't have enough room above the valve to mount the device, for example energetic pipelines, construction. Big problem is also hard working conditions such as high temperature, humidity, noise, acid gases etc., the device itself doesn't allows automatization of the process, which can be very unpleasant for the persons that are doing the testing.

SESITEST of the manufacturer Sempell, which overcomes the force with pneumatic system and cylinder. Compressor is filling air directly in the pneumatic cylinder, which is mounted onto the construction of the device which is mounted on top of safety valve. With great proportion of the areas of the pistons in pneumatic cylinder we achieve magnitude of the force that is bigger than the force of the spring. With sensors it's measured pressure in the pneumatic cylinder, pressure in the system and lift of the spindle of the safety valve. In this case also comes to the problems that are mentioned in the previously described known state.

Common characteristics of the known solutions is to overcome the force of spring with hydraulic or pneumatic drive and measuring the pressure in the system and lift of the spindle of the safety valve. Consequently, that means device of too big dimensions and need for heavy and unpractical hydraulic or pneumatic pump and proper pressure pipes. Problem with known devices is their big dimensions and consequently in many cases it's hard or even impossible to mount the device on the top of the safety valve and because of the weight of the pumps, pipes and the rest of the equipment it's hard or impossible to come to the tested valve.

According to the present invention, the described problems are solved with the device for testing safety valves driven by electromotor and reducing gearing over the snail and signal gearing to the moving screw, with which the force is achieved that overcomes the counterforce of the spring of the safety valve.

The invention will become apparent from the following description of the preferred embodiments and drawings illustrating:

Fig.1 - technical drawing of the device for testing safety valve of the first embodiment, mounted on the safety valve and electric connections to the electronic unit.

Fig.2 - detail of the technical drawing of construction of device for testing safety valve of the second embodiment, mounted on the safety valve.

Device for testing safety valves after invention after first embodiment is made up of:

Driving complex 31 :

- electromotor 1

- planetary reductor 2

- snail 3

- snail gearing 4

- bearing 5

Working complex 32:

- moving screw 6

- clamping head 7

Bearing structure 33:

- holder 8

- holding leads 9

- clamping frame 10

- screws 11

Safety valve 34: - spindle 12 - spring 13 - disc 19

- seat 20

- clamp 21

System 35 under pressure:

- pressure transducer 18

Safety valve 34 has inside spring 34, which pushes spindle 12 and disc 19 on the seat 20 of the valve 34, which assures closing position and consequently better tightness. Clamp 21 is in rigid connection with the housing of the safety valve 34. Top of the spindle 12 of the spring 13 is partly jutting out on the top of the housing and slides through fixed clamp 21 . Safety valve 34 has cover, which during working conditions protects clamp 21 and top of spindle 12 of spring that is jutting out of the housing. Cover has special lever that is sticked under pin 14 of spindle 12 of spring 13; with the lever we can manipulate with spindle 12 of spring 13 and clean the safety valve 34.

Safety valve 34 is mounted in the pressure loaded system 35 which is to be protected.

Bearing structure 33 comprises pressure loaded holding leads 9 of the mechanism, on which is on the top ortogonally put holder 8 of the driving mechanism, on the lovest end is parallel with holder 8 clamping frame 10, which is touching top of the safety valve 34 and serves for fixing the whole structure 33 on the safety valve 34. With clamping frame 10 with screws 11 of the clamping carrier the structure 33 is mounted on the neck of the safety valve 34. Because the structure 33 is pressure loaded, the clamping frame 10 must lay on the top of the housing of the safety valve 34, so that compensates the force, that is acting down. Screws 11 must be tighten enough, so that the whole structure 33 is firmly mounted on the safety valve 34, without any danger of falling down.

The height of holders of the driving mechanism is settled according to the clamping head 7 and pin 13 of spindle 12 of spring 13 and that is achieved with the holes in the holding leads 9 and holder 8. Fine adjustment of the height can be carried out with turning the clamping head 7, which can be done because of the metric outer thread on moving screw 6 and inner thread in clamping head 7.

On holder 8 of driving mechanism there is firmly fixed electromotor 1 , to which planetary reductor 2 is fixed directly, in accomplished case from the manufacturer MAXON MOTOR from Switzerland. Force can still be increased via reductor 2 and snail 3 to the snail gearing 4. To achieve as low friction as possible the snail gearing is made of brass, under which an axial loaded bearing 5 is mounted, all the parts being greased. The rest of the parts of the bearing structure 33, driving complex 31 and working complex 32 are made of inox steel with high mechanical properties, so that dimensions and weight are as small as possible, and also easier use of the complete device.

Through snail gearing 4 and axial loaded bearing 5, featured by trapezoidal thread inside of snail gearing 4, moving screw 6 with outer trapezoidal thread moves in the radial direction; the wedge prevents the moving screw 6 to rotate. On screw 6 there is in single axis fixed clamping head 7 in which there is spindle 12 of spring 13 of safety valve 34 clamped with the pin 1. Elements screw 6, clamping head 7 and spindle 12 are connected to one another in one axis, and they are strain loaded.

Electromotor 1 is high quality DC electromotor with defined and known characteristics of momentum in dependence of input current. On axis of electromotor 1 is optoelectronic giver with codes in raster preferably of 500 impulses per revolution. Electromotor 1 is wired via line 41 from electronic unit 15, impulses from optoelectronic giver are via line 42 led to electronic unit 15. Electronic unit 15, in present embodiment made by Remake D.O.A. Slovenia, transforms electric parameters into the form suitable for processing with computer. First electrical parameter via optoelectronic giver and via appropriate calculations features move, ie. lift of the spindle 12. Second parameter is input current of the electromotor and after previous calibration and calculation means the force on the moving screw or force, with which the complete device lifts the spindle 12.

On the system 35 under pressure, where a manometer for measuring system pressure is regularly mounted, electronic pressure transducer 18 is being mounted, in present embodiment made by VDO from Germany, which is functioning on the principle of changing properties of the piezzo crystal and measures pressure in the system 35. Pressure transducer 18 is connected with electric wire 43 to electronic unit 15, which transforms electric signal of transducer 18 into the form, suitable for processing with computer. For achieving necessary accuracy of the measurement, in practice the temperature sensor is added to the transducer 18 to compensate mistakes, caused by temperature changes.

Electric measuring signals are via wires 41 , 42 in 43 led to the electronic unit 15 which transforms the signals proceed them to the computer for the further processing and to the printer to print out the protocol of the measurement. Test

Test is based on measuring force on the spindle 12, which is via electromotor 1 increased with driving complex 31. When electromotor 1 is turning and propels the snail gearing 4 which consequently lifts the moving screw 6 and because of that spindle 12 of spring 13 is lifting and with that also the straining force increases. When the force, which is created by driving complex 31 , is equalized with force of spring 13 and force of pressure on disc 19 in system 35, which are acting in opposite directions, the safety valve 34 opens in that way that disc 19 separates from seat 20. This is the beginning of the opening or set pressure.

Electronic unit via wire 41 measures strength of the input current of electromotor 1 and consequently the force of lifting spindle 12. In the moment of beginning of opening or at set pressure of valve 34 because of beginning of leaking of pressure media, force decreases and with it also force on the spindle 12 and input current of electromotor 1.

With optoelectronic giver at the same time the angle of rotation of electromotor 1 is also measured and with that by calculation of transmission of driving complex 31 in every moment lift of the spindle of spring 12 and consequently disc 19 are also measured.

Pressure in the system 35 is at the same time measured by pressure transducer 18.

In this way electronic unit 15 via wires 41 , 42 and 43 records three electronically measured parameters, which are included in measuring characteristics of the safety valve. This are: lift of spindle 12, force on spindle 12 and pressure in system 35. According to these electronically measured values and known active closing area of the seat of the valve 20, electronic unit 15 or computer that is connected to it, in every moment calculates the measured characteristics of the valve 34 and also writes, plots and records the data by the following formulae:

force of test device set pressure = + system pressure active area of the seat

Technology allows automatization of the process from the start of the electromotor by pushing the button to the automatic stop of the electromotor after finished test - process. Accurate automatic or manual measuring of protective valve characteristics and records of the protocol, diagrams and results are enabled.

According to the second embodiment as shown on Fig. 2, the basic construction of device for testing safety valve is identical as it is in first embodiment. The only modification is, that sensor 36 is added in-between moving screw 6 and clamping head 7. Sensor 36 is electronic force measuring device, measuring the force with which the driving complex 31 lifts spindle 12 of spring 13 of safety valve 34. Electronic measuring signal of the sensor 36 is via wire 44 led to electronic unit 15. For achieving necessary accuracy on sensor 36 is in practice added temperature sensor for compensating the mistakes, that could be caused by temperature changes. Measurement after second embodiment goes similar to the first one, just that the force of driving complex 31 on the spindle 12 is measured directly with sensor 36 and not via input current of electromotor 1.

Advantages of described embodiments are:

According to the present invention the driving is solved with electromotor and reductor, which essentially reduces height of the device for testing safety valves.

With that also reduction of the number of parts of whole device on two basic - easy to transport port: mechanical part of the testing device and electronic transformer of signals with computer and printer is achieved, so that mounting and transporting of the equipment is essentially alleviated. Fully automatization of the testing process and registration is made possible, including the print out of the protocol. Because of the practically unlimited length of the connecting cables, the personal performing the test may move away from the testing point, even in to other room if necessary. Mentioned solutions allows simple transport and mounting, complete process of tests from mounting to dismounting is essentially reduced.

Claims

1. Device for testing and depicting characteristics of the safety valves during normal working process of the pressurized system, comprising driving complex with working complex, load bearing structure for mounting device on the safety valve, pressure transducer and electronic unit, characterized in that driving complex (31 ) comprises electromotor (1 ) with optoelectronic giver, reductor (2), snail (3), snail gearing (4) with inner thread and that within the said snail gearing (4) moving screw (6) with clamping head (7) is placed.

2. Device for testing safety valves as claimed in Claim 1 , characterized in that between moving screw (6) and clamping head (7) sensor (36) is placed.

3. Device for testing safety valves as claimed in Claim 1 , characterized in that the electric measuring signals of the input current of electromotor (1 ), of the position of optoelectronic giver and of the pressure of the system from pressure transducer (18) are wired to electronic unit (35).

4. Device for testing safety valves as claimed in Claims 1 and 2, characterized in that the electric measuring signals of force sensor (36), of position optoelectronic giver and of pressure in the system of pressure transducer (18) are wired to electronic unit (35).