GB1604709A

GB1604709A - Method of and apparatus for testing the fluid tightness of test pieces

Info

Publication number: GB1604709A
Application number: GB2162278A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1977-12-22
Filing date: 1978-05-23
Publication date: 1981-12-16
Also published as: DE2757318A1

Description

(54) A METHOD OF AND APPARATUS FOR TESTING THE FLUID TIGHTNESS OF TEST PIECES (71) We, ROBERT BOSCH GMBH., a German company of Postfach 50, 7000 Stuttgart 1, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a method of and apparatus for testing the fluid tightness of a test piece.

The invention is particularly, but not exclusively applicable to the testing of valves and injection nozzles, and the apparatus to be described may also be used to determine their operating pressure.

The invention the scope of which is defined in the appended claims, includes a method of testing the fluid tightness of a test piece disposed in a test system, the method comprising the steps of supplying fluid to the test system to bring the test piece up to a predetermined test pressure; monitoring the pressure at the test piece to produce electrical signals indicative thereof; closing the test system in response to an electrical control signal indicative of the test pressure having been reached;; operating a pressure restoring device in response to electrical control signals indicative of a pressure loss at the test piece due to leakage, the pressure restoring device including a displacement element adapted to be displaced in response to the pressure loss to reduce the volume of the closed test system in order to maintain said test pressure substantially constant throughout the test; and measuring the displacement of the displacement element to provide a measure of fluid leakage.

The invention also includes apparatus for testing the fluid tightness of a test piece comprising; a pump for delivering fluid to a test piece disposed in a test system to apply pressure to the test piece: a pressure sensor for measuring the pressure applied to the test piece, said pressure sensor being adapted to supply an electrical signal to computer means which is operable in response thereto to influence the pump to terminate fluid delivery to said test system and thereby close the system when said applied pressure reaches a preset test pressure;; a pressure restoring device operable in response to electrical control signals from said computer means indicative of a pressure loss at the test piece due to leakage, said pressure restoring device including a displacement element which is displaceable in response to the indicated pressure loss to reduce the volume of the closed test system to restore said test pressure; and means for measuring the displacement of the displacement element to provide a measure of fluid leakage.

In order that the invention may be well understood three embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows a diagrammatic illustration of testing apparatus; and Figure la is a graphical representation of pressure against time in a typical testing sequence.

A test piece is referenced 10 in Figure 1, and is for example a nozzle holder with an injection nozzle, which is disposed in a test system influenced by fuel from a delivery pump 11 through lines 12, 13. A valve 39, for example a non-return valve, is arranged in the line 12 beyond the delivery pump.

The test pressure generated in the lines 12, 13 also acts on a pressure sensor 14 from which a signal is transmitted to computer means in the form of a process computer 16 over an electric line 15. Furthermore, the line 12 leads to a displacement element designed as part of a pressure restoring device or metering unit 17. A spring metal bellows 18 is arranged in the latter device or unit such that the exterior or the bellows is compressed by the pressure medium located in the housing of the metering unit the pressure of which is equal to the pressure applied to the test piece 10 and sensed by sensor 14. A pressure accumu- lator 40 is also connected to the interior of the bellows 18.

The process computer 16 has an output 20 which leads to a regulator 21. The regulator 21 controls a motor 22 which can expand the metal bellows 18 through a drive 23. The pressure restoring device 17 cooperates with a displacement sensor 24 which is calibrated in volumetric units.

This calibration relates to leakage losses which can exist at the test piece 10. Thus, the amount of leakage can be read off directly at the displacement sensor; it can however also be transmitted to the computer 16 through an input 25. Furthermore, the desired value 27 of the test pressure is transmitted to the process computer through an input 26: this is the preset or desired pressure. Furthermore, a pulse generator 28 is provided from which an electric line 29 leads to the process computer 16. The pulse generator is influenced by the stream of liquid emerging from the test piece when the test piece reaches its operating pressure.

The computer 16 can be provided with a printer to provide a permanent record of the performance of each of the test pieces.

In the diagram according to Figure la, time is plotted on the abscissa and pressure on the ordinate. The control pressure P, the same as the test pressure, is represented by a chain dotted line. The opening pressure P0 of the test piece, which is of course higher than the test pressure, is represented by a dotted line.

The test piece 10 is influenced by the delivery pump 11 until the test or control pressure is reached. The pressure sensor 14 then signals this to the process computer which then delivers a signal for setting the pump. The valve 39 then closes the test system or chamber hermetically. If the diagram of Figure la is consideredqhe pressure has risen from Pro = atmospheric pressure to the test pressure P. It is then necessary for the test pressure to be held constant over the testing period tl despite possible leakage losses at the test piece 10.

This takes place in the following manner: when, due to lack of fluid tightness at the test piece. liquid escapes from the lines 12 and 13, the pressure therein drops, that is to say there is a difference between the desired value and the actual value, which is immediately transmitted to the process computer by the pressure sensor. The computer then delivers signals to the regulator 21 which switches in the motor and extends (stretches) the metal bellows 18 of the pressure restoring device 17 through the interposition of the drive. Due to the extension of the metal bellows, the pressure in the housing of the metering unit and with it that in the lines 12 and 13 is increased until the test pressure is once again reached, which is once again transmitted by the pressure generator to the process computer.When the test pressure is restored the motor 22 is switched off so that the metering unit is then actuated no further.

Thus, in this manner, it is possible to maintain the test pressure constant for the period tl. Due to the coupling of the pressure restoring device 17 to the displacement sensor 24, the amount of leakage can be read off directly. It can also be delivered to the process computer which either displays it on an oscillograph or on a printed sheet.

If it is also desired to test the opening pressure of the test piece, then, by switching off the motor 22 and switching in the delivery pump, the pressure is increased up to the opening pressure P which is illustrated in the diagram by a dotted line. At the instant of opening, a stream of liquid strikes the pulse generator. This is illustrated in the diagram by the chain double dotted line and can be recognised there as a peak.

It will be appreciated that for testing the opening pressure of the test piece, the amount of liquid available for metering must be greater than that of the leakage losses.

Mounting of the test piece must be such that it can be well ventilated. It is also preferable to provide measures such that when a particular leakage level is exceeded, the test is interrupted. In that manner, optimum testing times and objectives results are achieved.

It will be appreciated that the abovedescribed testing method has many advantages over previously proposed visual observation methods, in partciular it can be carried out fully automatically with high accuracy thereby avoiding the over-tiring of a human tester.

WHAT WE CLAIM IS:- 1. A method of testing the fluid tightness of a test piece disposed in a test system, the method comprising the steps of supplying fluid to the test system to bring the test piece up to a predetermined test pressure; monitoring the pressure at the test piece to produce electrical signals indicative thereof; closing the test system in response to an electrical control signal indicative of the test pressure having been reached; operating a pressure restoring device in response to electrical control signals indicative of a pressure loss at the test piece due to leakage, the pressure restoring device including a displacement element adapted to be displaced in response to the pressure loss to reduce the volume of the closed test system in order to maintain said test

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. sensed by sensor 14. A pressure accumu- lator 40 is also connected to the interior of the bellows 18. The process computer 16 has an output 20 which leads to a regulator 21. The regulator 21 controls a motor 22 which can expand the metal bellows 18 through a drive 23. The pressure restoring device 17 cooperates with a displacement sensor 24 which is calibrated in volumetric units. This calibration relates to leakage losses which can exist at the test piece 10. Thus, the amount of leakage can be read off directly at the displacement sensor; it can however also be transmitted to the computer 16 through an input 25. Furthermore, the desired value 27 of the test pressure is transmitted to the process computer through an input 26: this is the preset or desired pressure. Furthermore, a pulse generator 28 is provided from which an electric line 29 leads to the process computer 16. The pulse generator is influenced by the stream of liquid emerging from the test piece when the test piece reaches its operating pressure. The computer 16 can be provided with a printer to provide a permanent record of the performance of each of the test pieces. In the diagram according to Figure la, time is plotted on the abscissa and pressure on the ordinate. The control pressure P, the same as the test pressure, is represented by a chain dotted line. The opening pressure P0 of the test piece, which is of course higher than the test pressure, is represented by a dotted line. The test piece 10 is influenced by the delivery pump 11 until the test or control pressure is reached. The pressure sensor 14 then signals this to the process computer which then delivers a signal for setting the pump. The valve 39 then closes the test system or chamber hermetically. If the diagram of Figure la is consideredqhe pressure has risen from Pro = atmospheric pressure to the test pressure P. It is then necessary for the test pressure to be held constant over the testing period tl despite possible leakage losses at the test piece 10. This takes place in the following manner: when, due to lack of fluid tightness at the test piece. liquid escapes from the lines 12 and 13, the pressure therein drops, that is to say there is a difference between the desired value and the actual value, which is immediately transmitted to the process computer by the pressure sensor. The computer then delivers signals to the regulator 21 which switches in the motor and extends (stretches) the metal bellows 18 of the pressure restoring device 17 through the interposition of the drive. Due to the extension of the metal bellows, the pressure in the housing of the metering unit and with it that in the lines 12 and 13 is increased until the test pressure is once again reached, which is once again transmitted by the pressure generator to the process computer.When the test pressure is restored the motor 22 is switched off so that the metering unit is then actuated no further. Thus, in this manner, it is possible to maintain the test pressure constant for the period tl. Due to the coupling of the pressure restoring device 17 to the displacement sensor 24, the amount of leakage can be read off directly. It can also be delivered to the process computer which either displays it on an oscillograph or on a printed sheet. If it is also desired to test the opening pressure of the test piece, then, by switching off the motor 22 and switching in the delivery pump, the pressure is increased up to the opening pressure P which is illustrated in the diagram by a dotted line. At the instant of opening, a stream of liquid strikes the pulse generator. This is illustrated in the diagram by the chain double dotted line and can be recognised there as a peak. It will be appreciated that for testing the opening pressure of the test piece, the amount of liquid available for metering must be greater than that of the leakage losses. Mounting of the test piece must be such that it can be well ventilated. It is also preferable to provide measures such that when a particular leakage level is exceeded, the test is interrupted. In that manner, optimum testing times and objectives results are achieved. It will be appreciated that the abovedescribed testing method has many advantages over previously proposed visual observation methods, in partciular it can be carried out fully automatically with high accuracy thereby avoiding the over-tiring of a human tester. WHAT WE CLAIM IS:-

1. A method of testing the fluid tightness of a test piece disposed in a test system, the method comprising the steps of supplying fluid to the test system to bring the test piece up to a predetermined test pressure; monitoring the pressure at the test piece to produce electrical signals indicative thereof; closing the test system in response to an electrical control signal indicative of the test pressure having been reached; operating a pressure restoring device in response to electrical control signals indicative of a pressure loss at the test piece due to leakage, the pressure restoring device including a displacement element adapted to be displaced in response to the pressure loss to reduce the volume of the closed test system in order to maintain said test

pressure substantially constant throughout the test; and measuring the displacement of the displacement element to provide a measure of fluid leakage.

2. Apparatus for testing the fluid tightness of a test piece comprising; a pump for delivering fluid to a test piece disposed in a test system to apply pressure to the test piece; a pressure sensor for measuring the pressure applied to the test piece, said pressure sensor being adapted to supply an electrical signal to computer means which is operable in response thereto to influence the pump to terminate fluid delivery to said test sysem and thereby close the system when said applied pressure reaches a preset test pressure;; a pressure restoring device operable in response to electrical control signals from said computer means indicative of a pressure loss at the test piece due to leakage, said pressure restoring device including a displacement element which is displaceable in response to the indicated pressure loss to reduce the volume of the closed test system to restore said test pressure; and means for measuring the displacement of the displacement element to provide a measure of fluid leakage.

3. Apparatus as claimed in claim 2, wherein the measuring means comprises a displacement sensor cooperable with the displacement element, the sensor being calibrated in volumetric units for indicating the amount of fluid leakage.

4. Apparatus as claimed in claim 2 or 3, further comprising means for measuring the operating pressure of the test piece, said operating pressure measuring means comprising means for increasing the pressure above the test presesure, and a pulse generator for detecting a stream of fluid issuing from the test piece due to its operation and for supplying a corresponding signal to the computer means.

5. Apparatus as claimed in any one of claims 2 to 4, wherein the computer means is adapted to control a regulator for controlling a motor which actuate the displacement element.

6. Apparatus as claimed in any one of claims 2 to 5, wherein the displacement element comprises spring bellows arranged in a fluid tight housing, the bellows being adapted to be subjected externally to the pressure applied to the test piece such that whilst a constant test pressure is being maintained in use the bellows expands when the pressure drops below the test pressure.

7. Apparatus as claimed in any one of claims 2 to 6, wherein a pressure accumulator is connected to the displacement element.

8. Apparatus as claimed in any one of claims 2 to 7, wherein a valve is positioned downstream of the delivery pump for cutting off the pump from the test system.

9. A method of testing the fluid tightness of a test piece substantially as herein described with reference to the accompanying drawings.

10. Appartus for testing the fluid tightness of a test piece substantially as herein described with reference to the accompany ing drawings.

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