200 MPa He Pressure Regulators
The 2kbar Gas Pressure Controller supply continuously loaded high-pressure cells and Paris-Edinburgh presses with helium at a pressure ranging from 100 to 2 kbar (0.2 GPa). The gas is compressed with a standard single-stage diaphragm compressor from Nova-Swiss and stored in a buffer volume. The stabilization and ramps of pressure are performed with two innovative pneumatic valves patented by CNRS (patent #04 00 515). One valve is used to decrease the pressure and the other one to increase the pressure in the cell or press. They are actuated by a Eurotherm 2704 controller at a maximum rate of 30 bar per minute.
The operating principle of these novel valves is based on the elastic deformation of materials and is characterized by the absence of a stuffing box (0-ring). This is a real innovation for a flexible seal between the valve body and the needle stem is a source of many problems: leaks, pollution, and above all large friction effects requiring high force for opening/closing the valve and caus- ing large hysteresis.
The compressor, valves, controller and related electronics are packed in a crate that is easily moved to instruments. It also features two rollers of cables (380V and compressed air) and an external platform onto which a bottle of helium can safely be attached and exchanged. Remote operation is possible using the Modbus serial communication protocol (RS485 serial port or Ethernet).
After opening manually the helium bottle, a valve is automatically opened once the pressure delivered to the crate reaches 110 bar. A second valve is also opened when the pressure of the compressed air line reaches 6 bar. These two valves must be opened to put the crate into operation. The pressures are indicated on the synoptic.
The helium gas is filtered twice and goes through a check valve. It is then compressed with a Nova-Swiss 3 kbar single-stage diaphragm compressor. A high-pressure gauge located at the exit of the compressor returns the output pressure to the Eurotherm. The gas is stored in a buffer volume whose pressure is maintained 150 bar above the setpoint requested by the user. The Eurotherm controller opens the CNRS valve (VP1) to increase the pressure in the cell or press. It opens the CNRS valve (VP2) to decrease the pressure.
When there is an overload of pressure on the sample, a power cut, a compressed air cut or a lack of gas in the bottle, the low and high pressure circuits are automatically evacuated thanks to the valves operated by the mechanical pressure gauges. A 0.21 GPa relief valve located on the sample injection line and a kill switch complete the security system.
- Put the crate on a flat floor, the nearest to the high-pressure cell or press.
- Unroll entirely the electric extension available at the back and plug it to 380V. Check that the "Plugged In" light is on.
- Unroll the pipe of compressed-air and plug it to the line available on the instrument. Check that the pressure is above 6 bar (required to ensure a smooth operation of the crate). If necessary, open the valve on the compressed air line.
- Close the manual valves "Buffer Relief Valve", "Helium Relief Valve", "Compressed Air Relief Valve" and "Sample Cell".
- Switch on the crate by actuating the "Power" button and wait until the controller is ready.
- Open the bottle of helium located at the back of the crate and tune the pressure reducer to about 50 bar.
- Check that the limits of the pressure gauges (red arrows) are set to 5.5 bar (compressed air), 100 bar (helium) and 2100 bar (sample cell). It is absolutely forbidden to change that settings.
- The pressure gauges indicate the actual pressures: about 6 bar for the compressed air line and 100 bar for the helium line.
- With the pressure reducer of the bottle of helium, tune the pressure gauge of the control panel (synoptic) to 150 bar.
- Press the "Fault Acknowledgment" button twice for switching off the "Helium Fault" and "Compressor Fault" lights.
- If there is no default, the red lights are switched off and the pressure controller is ready.
- If necessary, to flush the helium line, open the "Sample Cell" valve, enter a setpoint of about 2 bar on the Eurotherm and wait until helium flows out of the capillary, enter a setpoint of 0 and close the valve.
- Plug the capillary to the high-pressure cell or press, open the "Sample Cell" valve.
With the arrow keys of the Eurotherm controller, enter the requested pressure. Once the "Sample Setpoint" is indicated on the display, the compressor starts. After a few minutes, if there is no leak, the pressure is regulated around the setpoint value. Here is the time expected to get to pressure:
- about 3 minutes to reach 500 bar (50 MPa)
- about 5 minutes to reach 1000 bar (100 MPa)
- about 20 minutes to precisely stabilize the pressure at 2000 bar (200 MPa)
For increasing or decreasing the pressure on the sample, modify the "Sample Setpoint" value with the arrow keys on the Eurotherm.
For exchanging the helium bottle while the controller is in operation:
- Close the helium bottle.
- Open and close the pressure reducer of the bottle to purge the gas, until 0 bar.
- Dismount the pressure reducer and extract the bottle from the platform of the crate.
- Mount and attach the new bottle on the platform of the crate.
- Screw the pressure reducer by hand (without tool).
- Open the bottle and tune the pressure regulator so that 150 bar is indicated on the control panel (synoptic).
For releasing the pressure, enter a "Sample Setpoint" of 0.00 with the arrow keys on the Eurotherm and wait. It takes about 35 minutes when starting from 100 MPa (1000 bar) when the temperature is high enough to truly release the pressure in the cell. If the temperature is too low, one must warm up the cell so as to follow the solidification curve of He.
Once the pressure at about 0:
- Close the helium bottle.
- Open slowly the "Buffer Relief Valve".
- Check that the pressure decreases to zero on the "Sample Cell" mechanical gauge before disconnecting the capillary.
- A big noise can be produced when the rack is switched off (relief of the compressed air line and helium buffer).