TITLE Pressure calibration pump apparatus TECHNICAL FIELD The present invention relates to a pressure calibration pump apparatus for generation of vacuum or pressure, which pump apparatus comprises a cylinder with an outlet valve and a displaceable piston operable by means of a piston rod, the forward end of which carries a conical inlet valve located at the centre of the piston and being provided with channels for supply of a calibration medium, wherein the piston rod and the piston are interconnected in such a way that the alteration of the direction of movement of the piston rod at the respective turning point of the piston movement, involves the opening and closing respectively of the inlet valve. The invention also relates to a method for pressure calibration of a pressure sensor by means of a liquid state medium, by means of a pump apparatus comprising an outlet valve and an inlet valve as well as channels for supply of the medium, wherein the outlet and inlet valves are connected to a valve head, to which the pressure sensor is attachable, and which comprises a valve spindle that is adjustable in the head to enable the switching between the functions of pressure and vacuum generating and which valve head is provided with a first connection for the pressure sensor as well as a second connection for the calibration medium, facilitating handling said medium in a closed-circuit system.

STATE OF THE ART As a result of increasing demands for safety and economy, there

is a growing need for calibration within the industry.

Calibration work is often performed outdoors in an area which may consist of several hectares amongst the pipes and containers of a plant, often high over the ground surface. In such an area there are often thousands of so called pressure transmitters that are connected to the system in order to supervise or control a process. For the purpose of calibration of these pressure transmitters, there are available light, portable and self-supporting instruments comprising a pressure and vacuum generator together with an accurate pressure gauge. The manufacturers of calibrators develop and implement intelligent up-to-date quality systems with to an ever increasing extent more accurate small portable pressure gauges. However, the pressure generator side, thus the pump, has not benefited from as much attention in spite of the need for high vacuum, normal and high pneumatic pressure and hydraulic water pressure up to 200 bar.

When calibrating ! an pressure transmitter transmitter functions in the vacuum area, accurate calibration requires a calibration pressure which is very close to 100% vacuum, 0 bar or kPa. However, with the available portable vacuum pumps it is not possible to create a sufficiently high degree of vacuum.

Therefore, one has to confine oneself to a point near a good half of the absolute vacuum and to calibrate the zero scale mark of the transmitter, absolute vacuum = 0 bar or kPa, after a calculation based upon the obtained calibration pressure.

Occasionally, these transmitters must be dismounted and calibrated in a stationary calibration room where a suction vacuum apparatus is available. About 99,6% vacuum may be obtained with such an air operated vacuum pump which is 0,004

bar or 4 mbar or also-996 mbar. Even then the zero scale mark must be simulated after a calculation, but because the distance to the absolute vacuum is very small, the error will be insignificant.

With an ordinary hand operated, pneumatic calibration pump for medium pressure range, you can reach a maximum pressure of 15- 20 bar. The cylinder diameter is between 25-28 mm and the piston is subject to a mechanical pressure force of about 1300 N at 20 bar. This high force is created precisely at the end of the piston movement, depending upon the physical properties of the gases during compression. This is possible due to the progressive lever system of the leg mechanism which increases the hand force power to the piston 3-4 times. Then the counter force will be so large that it will be very difficult to press the two legs together. It would be possible to reduce this counter force by reducing the cylinder diameter. The active volume of the pump,, that is the cylinder diameter, must be large in order for the pumping process not to be too time consuming during calibration. Partly this depends upon the other passive volumes of the equipment, like the valve housing with channels, the fine adjustment volume, the exhaust valve, the connectors and the connecting tubes have large dimensions and diameters and therefore comparatively large gas-filled volumes in comparison with the small volume of the very pressure transmitter. These passive volumes may be defined as harmful volumes with reference to the capacity of the pump.

In process plant there are to some extent pressure transmitters which operate with up to 40 bars pneumatic pressure. Because it is not possible to generate such high pressures with a common

pneumatic hand pump, a high pressure cylinder is used for this purpose with a reduction valve or a hydraulic hand pump. The instrument engineers demand pneumatic hand pumps with up to 40 bars maximum pressure because even a small compressed-air cylinder is heavy and awkward to carry around and a hydraulic hand pump leave hydraulic fluid behind in the pneumatic system.

During calibration of pressure transmitters in chlorine and oxygen plants, there are problems with moisture in the calibration air and problems with oil and dust. Because the available pneumatic calibration pumps that are available do not have any separate insulated calibration medium inlet, it is necessary to connect a container with a moisture absorbing substance or a dust filter at the pressure side, at the outlet of the pump. This results in a substantial increase of the gas- filled volume and is as such harmful extending the pumping process considerably. During calibration of pressure transmitters in nuclear power plants there are special requirements for materials for the cylinder, piston, water container and channels of the pump.

SUMMARY OF THE INVENTION One object of the present invention is therefore to provide a handy portable calibration pump which makes it possible to reduce the above described drawbacks.

THE SOLUTION For this object, the invention is characterized in that the cylinder is provided with sealing means for sealing between the intake side of the piston and the external atmospheric pressure.

By this design of the piston cylinder, it is possible to achieve

very high values for both vacuum and pressure. This means that it is possible with the same pump to cover the entire pressure range which is frequent in practical field calibration. The piston apparatus with valves enable generation of pressures from near absolute vacuum up to 40 bar. According to prior art, a separate pump is used for vacuum, another pump for the medium pressure range and still another pump for hydraulic high pressure calibration.

According to a preferred embodiment of the invention, the piston is divided into a front member and a rear member, wherein the rear piston member forms the sealing which is substantially rigidly connected to the piston rod and provided with sealing means towards the wall of the cylinder. Alternatively, the sealing may be rigidly connected to the cylinder wall and provided with sealing means towards the piston rod.

The outlet valve and, the inlet valve are preferably connected to a valve head which comprises a valve spindle movable within the head and enabling the switching between the functions of pressure and vacuum generating.

According to another preferred embodiment of the invention, the valve spindle is provided with a pressure balancing valve for pressure balancing towards an external pressure.

The valve head may preferably be provided with a first connection for a pressure sensing means as well as a second connection for a calibration medium. Preferably, the valve head is also adapted for handling calibration medium in a closed-circuit system. This also

makes it possible to pre-treat the calibration medium by filtering or by chemical treatment.

According to another preferred embodiment of the invention, the piston rod is operable by means of an adjustable lever system which comprises a spring-loaded knee action unit. This enables hydraulic operation and at the same time provides better ergonomics by the variable adjustment of the handle width.

The lever system preferably comprises a twist grip facilitating infinitely variable adjustment of the stroke of the piston from a few millimetres to full stroke. The twist grip preferably comprises a trapezoid thread which engages a lead-through sleeve and an end stop at the piston rod having a corresponding trapezoid thread. The twist grip may at opposite sides be provided with two axially longitudinal guide slots in which two guide pins run, being attached to the housing of the pump to prevent the lead- through sleeve from rotating with the twist grip.

The method according to the invention is characterized in that the valve spindle to begin with is positioned in the vacuum generating position, that the air is sucked away from the inner channels of the pump and the valve spindle as well as from the connection of the pressure sensor, that the air that has been sucked away is evacuated to a container for the calibration medium in the course of pressurising said medium, wherein the valve head is partly filled by the medium, that the valve spindle is moved over to the pressure generating position, after which the inner channels of the pump and remaining parts of the valve head is filled with the medium, and that the valve spindle is positioned in the pressure generating position allowing

increase of the pressure by pumping to a suitable level for calibration.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will in the following be further described in a non- limiting way with reference to the accompanying drawings in which: Fig. 1 shows a section of a first embodiment of the pump apparatus with the valve head and the flow channels, the inlets and outlets, the fine adjustment volume as well as the handle mechanism with the screw means for the adjustable stroke, Fig. 2 shows an enlarged partial section of the piston apparatus with the friction controlled inlet valve, Fig. 3 shows the piston apparatus corresponding to Fig.

2 while being moved in the direction upwards in the figure, Fig. 4 shows an alternative embodiment of the piston apparatus, and Fig. 5-7 shows the pump apparatus in three different modes of function during calibration by means of a hydraulic medium.

Theoretical description There are two factors that obstruct and limit the ability to reach a high degree of vacuum with a simple hand operated piston pump. The first obstruction is the pressure threshold in the inlet valve which often has a comparatively small opening area and which is closed by means of a spring-load and which has a typical threshold value of 0,2-0,4 bar.

The limit value may be calculated as: P threshold in = spring-load/valve area The second obstruction depends on the physical conditions with reference to the cylinder, the piston, the sealings as well as the design of the inlet and outlet valves. They must be designed so that the intake gas or air is evacuated as completely as possible when the piston reaches the cylinder bottom. This physical relationship is described by Boyle's law: p x V = constant or: pi x V1 = pi x V2 where P1 = cylinder pressure before the piston stroke V1 = cylinder gas volume before piston stroke P2 = cylinder pressure after piston stroke V2 gas volume in cylinder after piston stroke, i. e. residual volume On the other hand, the pressure threshold of the outlet valve is no significant factor for reaching a high degree of vacuum. Thus it should be spring-loaded and have a small diameter. If you exclude the pressure threshold of the inlet valve and has an outlet valve with a pressure threshold of 0,5 bar, which is a high value, it is evident that it is the relationship V2/V1, which in practice may be written as 0,01, and which decides the maximum vacuum value in the following manner: Pvacuum = V2/V1 x Pthreshold out if Pthreshold out = 0,5 bar and V2/V1 = 0,01 becomes

Pvacuum 0, 01 x 0,5 bar = 0,005 bar = 99,5% vacuum When the residual volume V2 is very small, the end pressure P2 of the intake thin gas is nevertheless comparatively large, which enables the compressed gas volume to easily pass through the spring-loaded outlet valve and thus a very little amount of gas remains inside the cylinder. This may be written: P2 = P1 x V1/V2 if V2 = 0 P2 = becomes indefinitely large The gas is rapidly evacuated from the pipe and from the connected pressure transmitter when repeating these piston strokes during pumping as these volumes are only a few cm3.

Thus, the obtained vacuum pressure directly proportional to the remaining volume V2 which represents the residual gas volume left in the cylinder after each piston stroke and because V2 may be made very small, the reached vacuum pressure depends in practice for the most part of the first-mentioned pressure threshold of the inlet valve. In a vacuum pump with spring- loaded inlet valve, it is the pressure threshold of the inlet valve that constitutes a problem and prevents from reaching a high degree of vacuum. If the inlet valve is controlled by the friction force between the piston sealing and the cylinder wall, the inlet valve has no pressure threshold. If the residual volume V2 at the same time may be minimised by the design of the piston to 1-2% of the total cylinder volume V1, it is then possible to generate a degree of vacuum corresponding to 98-99 % vacuum.

DETAILED DESCRIPTION OF THE INVENTION In the drawings, 1 designates a cylinder and 2 the front part of the piston, a so called primary piston, with its sealing 3. In the centre of the primary piston there is a conical aperture 4 that opens out in the direction backwards. A taper 5 has been adapted to this conical aperture and being provided with an O- ring sealing 6. This forms the movable part of the inlet valve and is attached to the front end of the piston rod 7. During pumping the taper 5 presses the primary piston 2 in the direction forward and the 0-ring sealing 6 seals. In the middle of the piston rod 7 there is a channel 8 opening at the taper 5 immediately behind the 0-ring seal 6. In the rear end of the channel there is a tube connection 12 from which a tube 21 leads to the calibration medium inlet 22 or by vacuum operation to the calibration outlet 38 and further on to the subject of the vacuum calibration.. When the piston rod 7 is pulled back, downwards in the drawing, the pressure taper 5 with the O-ring seal 6 is distanced from the conical seat 4 in the primary piston 2 which is held back by the action of the sealing friction against the cylinder wall 1. By this the inlet valve 4, 5,6 is opened and the cylinder is freely filled through the inlet channel 8. When the piston rod 7 has moved backwards about 1 mm, the rear edge of the taper 5 which has a larger diameter than the piston rod reaches a locking ring 9 which is positioned close to the taper attached to the rear part of the primary piston. By the stop function of the locking ring 9, the primary piston 2 now follows backwards with the movement of the piston rod 7. The inlet valve is still held open because the taper 5 is about 1 mm from the sealing in the conical aperture 4, and the

cylinder is filled with air or fluid. Behind the primary piston 2 there is a so called secondary piston 10 with a sealing 11 against the cylinder wall 1 and it is securely attached and sealed onto the piston rod 7. The object of the secondary piston is to insulate the primary piston from the external atmospheric pressure and to prevent this from influencing the rear side of the primary piston 2 with its pressure force. During vacuum pumping, when operating with a pressure below the atmospheric pressure, there is a pressure difference between the front and the rear end of the piston which creates a force which pushes the piston forward. If the secondary piston 10 was absent, the compressive force of the atmospheric pressure would act on the primary piston 2 from behind and hold the inlet valve open even during the compression phase after a certain vacuum pressure has been obtained at the inlet. This would happen when: (Pa-Pv) x (Ac-Av) > Ff, where Pa = atmospheric pressure Pv = vacuum pressure at inlet Ac = cylinder area Av = opening area of inlet valve Ff = friction force between cylinder and piston sealing Fig. 4 shows an alternative embodiment where the sealing is rigidly attached to the cylinder wall and provided with sealing means 11 towards the piston rod 7.

With the above described piston arrangements, it is also possible to generate positive pressure. Because the inlet valve does not have a pressure threshold, the intake air has optimal

atmospheric pressure and volume. Thus, the cylinder diameter may be reduced compared to models having a spring-loaded inlet valve. This facilitates the generation of high pressure. The cylinder 1 with sealing means 11 that forms a sealing between the intake side of the piston 2 and the external atmospheric pressure provides advantages that appears when there is a need for a high degree of vacuum or pressure and when special gases, dust free or dry air or water and other fluids are needed for calibration and control, or for research.

The above described pump construction in combination with rust- resisting material and composites meets the demands for an universal pump which is needed on the market.

USE OF THE PUMP APPARATUS IN A CLOSED-CIRCUIT CALIBRATION SYSTEM Pressure mode: A channel 8,12,21 runs from the piston with the friction controlled inlet valve to the main valve 23-37 which is a screw controlled valve body having two mode positions. In the pressure mode, the valve body has been screwed clockwise to its end position and the intake air or fluid is drawn from the intake tap 22 to the main valve tap 30 and further through the main valve to the tap 29 and to a tube 21 the other end of which is connected to the tube tap 12 in the rear end of the piston rod. It is possible to connect a fluid or gas container to the inlet tap 22 or if calibrating with air, a dust or drying filter. The intake gas or fluid is drawn further on through the piston rod channel 8 and the inlet valve 4,5,6 to the cylinder 1 continuing from there through the outlet valve 20 again through the main valve from the tap 28 to 36 and further on to the fine adjustment volume 41 and through a tap 40 in the other wall of the fine adjustment volume directly to the calibration

tap 38 and to the measurement tap 39. When turning the valve screw 32 anticlockwise which screw is attached to the piston spindle 35, the conical pressure balancing valve or relief cock 34 is opened by means of the screw thread 33, which reduces the pressure and the gas or fluid is conducted to a particular drainage tap 27.

Vacuum mode: When screwing the piston spindle 35 with the main valve screw 32 six turns anticlockwise, it moves over to the left end position and the pump is transformed into a vacuum pump. The process is partly reversed. The connection tube from the vacuum pressure transmitter is connected as before to the calibration tap 38. The tap 39 is a measurement tap. The drawn gas passes through the fine adjustment volume 41 and further through the main valve tap 36 to the tap 29, because the high pressure seal 24 is positioned to the left of the tap 36, and then passes further on through the pump to the main valve tap 28, and from there through the open pressure balancing valve 34 out through the drainage tap 27. When turning the valve piston spindle 35 about one turn clockwise after vacuum calibration, it moves to the right in the drawings and valve port is opened which is formed by the sealing 25 then being positioned to the left of the point 37 at the calibration medium inlet 30. Then gas is drawn into the system through the inlet tap 22 and the gas flows directly through the main valve, from the tap 30 to 36 and through the fine adjustment volume 41 to the current vacuum pressure transmitter which is connected to the calibration tap 38. Due to that the gas is drawn through the inlet tap 22, it may be filtered or dried if this is required. The end sealings 23 and 26 prevent gas or fluids from leaking out or in. Thus, the calibration system is completely closed-circuit if so

desired. This enables the use of special for example hazardous or expensive gas or fluids and also allowing these to be collected after calibration.

All unnecessary space inside the pump which must be filled with gas, as the fine adjustment volume, the valve housing, the channels, the pressure and measurement taps, the adapters as well as the volume inside the connecting tubes are detrimental volumes with reference to the capacity of the pump. This has been paid attention to in the new construction. This enables the pumping phase to be reduced in spite of the high maximum pressure and in spite of that the cylinder volume is somewhat smaller than for the portable hand pumps which are available.

The cylinder area is halved and this raises the pressure to the double.

The stroke of the piston may be adjusted by means of a twist grip 14 at the centre of the pump. At the inside of the radially slot guided 17 twist grip, there is a trapezoid thread 16 which screws the lead-through sleeve and end stop 18 of the piston shaft forward or backward. The lead-through sleeve 18 has a corresponding trapezoid thread, on its outer surface as well as two longitudinal guide slots 15 in which two guide pins 19 run that are attached to the housing of the pump. The guide slots prevent the lead-through sleeve from rotating with the twist grip 14 and at the same time function as a range limit stop. This property is in the first place needed when using the pump as a hydraulic high pressure pump. When the stroke is small, it is possible to generate comparatively high hydraulic pressures due to the progressive power transmission of the knee action unit 13. The final pressure rise during hydraulic operation is done

with the assistance of the fine adjustment volume 41 which then acts as a screw pump. The piston area of the fine adjustment volume is only 0,5 cm2 which at 200 bar corresponds to somewhat above 1000 N force on the volume piston but only about 20 N of torsional moment at the volume control. The adjustable stroke also provide a feature which improves the ergonomics of the handles. A person with small hands may reduce the stroke a few millimetres to get a more comfortable grip.

HYDRAULIC PRESSURE CALIBRATION Generally, air easily enters the system when opening the calibration tap for a hydraulic pressure transmitter. Especially if the channels are long, the fluid flows out and it may be difficult to get the air away from the system when the calibration pump is connected and the calibration fluid is pumped in. There is a bleeder screw for this purpose, because of the forming of so called air pockets, the bleeding process is considered to be troublesome.

The vacuum and pressure pump according to the invention with its valve apparatus may advantageously be used for these occasions.

The pump is connected with ils'tube to the calibration tap, the valve spindle 35 (Fig. 5) is turned to the vacuum mode and air is sucked away from the tubes and from the pressure transmitter.

When connecting the drainage tap 27 of the pump to the inlet tap 22 the evacuated gas passes through the fluid 43 (Fig. 5) to the top 44 of the container 42 where the gas pressure rises. The pressure relief valve 46 protects the container and by controlling the gas pressure so that it does not rise too much.

This increased pressure presses the fluid down through the

channels 27 and 30 to the mode selector valve 31 and through the channel 28 all the way to the outlet valve 20. The density difference also promote this.

Then the valve spindle 35 (Fig. 6) is turned clockwise about a turn and injects calibration fluid 43 from the container 42 through the inlet tap 22 and further through the channels 30-37- 36 to the vacuum chamber. The increased gas pressure 44 in the fluid container 42 contributes to a rapid flow of the fluid to the pressure transmitter. Also the actual pump is filled with fluid through the channels 29-21-12. The stroke adjustment 14 must be adjusted to minimum stroke (Fig. 6) in order to enable hydraulic pumping with a high power output through the handles.

If the calibration channel or the pressure transmitter has a large volume, the capsule 45 of the container 42 must be opened in order to maintain the flow pressure by means of the external atmospheric pressure. If there is no available external atmospheric pressure, (below water or in outer space) the container must be sufficiently large and strong so as to be able to contain enough pressure or some other apparatus for the fluid flow.

When the calibration channel is filled, the valve spindle 35 (Fig. 7) is turned over to the pressure mode and the pressure is raised with the pump up to some multiples of ten bar and then the pressure increase is continued up towards several hundred bar with the pressure adjustment volume.

Because of the ability to lower and remove about 98% of the air from the calibration circuit, the resistance to the increasing

pressure is more compact and more stable since only a small amount of air is mixed with the calibration fluid due to the influence of the pressure.

The method may also be used with advantage when a hydraulic system should be ventilated and then be filled with a hydraulic fluid.