Tony Withers: Lab: Piston Cylinder SOP

How to Set Up a Piston Cylinder Experiment

Reserve a piston cylinder for the duration of your experiment using the online calendar

The Basics: Terminology

Stack	Carbide Spacer	Shim	Piston	Bridge	Pressure Plate
Thermocouple Plate Insulator	Thermocouple Plate	Slotted Plate	Large Spacer	Upper Insulator	Small Spacer
Graphite Disk	Cell Assembly	Base Plug	Thermocouple	Sample (Lower) Ram	Endload (Upper) Ram

The Basics: Hydraulic System

The electric and hand operated hydraulic pumps are both connected to the same hydraulic line. The valves A main and B main isolate each of the piston cylinders. Turning the valve on the right side of the hand pump clockwise prevents hydraulic fluid from draining back into the tank and thus enables pressure generation with this pump. Likewise, when the lever of the electric pump is pushed to the left, hydraulic fluid will not drain back into the tank of the electric pump. Keep the hand pump valve closed at all times other than when refilling the tank. In general, the electric pump is used to close the daylight at the beginning of an experiment, and the hand pump is used for controlled pressurisation. When the hydraulic cylinders are retracting, the valve of the electric pump must be open so that hydraulic fluid will return to the tank of this pump, which is the main hydraulic reservoir for the system. You should always make sure that the tank of the hand pump is filled before the start of an experiment. Close the main valves that isolate PC A and PC B. Open the dust cap to check the fluid level, close the electric pump valve and open the hand pump valve. Run the electric pump until the hand pump tank is full, close the hand pump valve and replace the dust cap and turn to the vent position.

Standard Operating Procedure

Preparing the standard cell assembly

• Make sure that all of the MgO pieces fit into the graphite furnace and that the alumina thermocouple sleeve fits through both the base plug and the MgO.
• Drill a hole in the 19mm piece of MgO to fit your capsule. Use a carbide end mill or a diamond drill to make a flat bottomed hole.
• Fire the MgO pieces at 1000 °C for ~12 h.
• Make the thermocouple. Bend the wires slowly using flat nosed pliers. The wires are very brittle, so be careful not to crack them. Use Duco cement to seal the holes at the top end of the insulator tube.

• Take the MgO out of the furnace. Allow it to cool under vacuum in a desiccator for 15 min. The MgO should not be taken out of the desiccator until the assembly is ready to load.

Building the stack

• Locate the carbide spacer in the centre of the lower ram and place a shim on top of the spacer.
• Place the bridge on top of the spacer without displacing the shim. Make sure that the surface of the bridge is clean and that the o-rings are in place. If necessary, remove the o-ring, wipe it clean and apply vacuum grease before returning it to its groove.
• Clean the piston and insert it into the hole in the bridge so that it rests on the shim.
• Clean the pressure plate. Look carefully for cracks in the core and make a note of the number and nature of the cracks.
• Lubricate the core of the pressure plate with moly-lube (thinnest possible coating) and place the pressure plate over the piston.
• Push the graphite disk in to the core.
• Take the cell components out of the vacuum desiccator. Insert the space filling MgO, the capsule, the 1mm disk and the 12mm MgO with the hole for the thermocouple tube into the furnace. Slide the furnace into the BaCO3 sleeve.
• Roll some lead foil to flatten and smooth it, and cut a piece of the correct size to wrap around the BaCO3 without overlapping.

• Place the furnace inside the BaCO3 sleeve. Wrap the BaCO3 with Pb-foil. The assembly goes inside the pressure vessel. Put the base plug and the Pyrex sleeve on top of the cell and the push it all the way down.

• If the top of the base plug is not flush with the top of the pressure plate, close the valve of the electric pump and the endload (sample) ram, open the main valve of your piston cylinder and close that of the other piston cylinder and open the sample (lower) ram valve. Pump very slowly with the hand pump until the base plug rises to the top of the pressure plate. Close the sample ram valve.

• Put the thermocouple plate insulator on top of the base plug. The hole of the mylar should be perfectly aligned with the base plug. A small amount of silicone grease can be used to make sure that the insulator stays in place.

• Make sure that there are no stray pices of broken thermocouple ceramic lodged inside the hole in the thermocouple plate. Clean the thermocouple plate and position on top of the pressure plate.
• Use the aligning pin to make sure that the hole in the thermocouple plate is aligned with the hole of the base plug. When perfectly aligned, the pin should slide all the way in without much resistance:

• Insert the thermocouple through the hole in the thermocouple plate, make sure that it goes all the way in and is touching the 1mm MgO disk. Record the length of thermocouple sticking out above the thermocouple plate (should be ~10 mm). The wires should exit the thermocouple plate pointing to the side or the rear (so that in case of catastrophic failure you won't be hit in the eye by ejecta).

• Place the slotted plate over the thermocouple plate. Align the slot toward the side.
• The large spacer with the power cable attachment goes on top of the slotted plate.
• The plastic insulator and the smaller steel plate (PC B only) sit on top of the large spacer.
• You should now be ready to close the daylight and pressurize the stack. Before you continue, pause to check that everything is in position. There should be two pieces of insulating plastic in the correct positions within the stack. Connect the thermocouple wires and make sure that the thermocouple junction is closed.

Increasing pressure...

• Open the MAIN valve for your piston cylinder, and close that of the other. Close the sample (lower) ram valve, open the endload (upper) ram valve. Run the electric pump to close the daylight before using the hand pump to increase the pressure to about 1000 psi. Close the endload (upper) ram valve.
• Attach the water hoses. The short hose connects the bridge to the thermocouple plate. The two main hoses in the back should be attached to the thermocouple plate and the bridge. Follow the color code: water enters at the bottom and leaves at the top. Give the hoses a tug to make sure they're properly attached.

• Attach the power cable. Make sure the connection is tight.

• Make sure that the drain valves are closed. Turn the water on. Open the water out valve first, followed by the water in valve.
• Feel the water flowing through the hoses -- oooh.
• If the low level warning light comes on, refill the chiller with coolant.

• Open the sample (lower) ram valve and start to pressurize using the hand pump. The end load and sample load are increased in tandem. Check the force balancing chart for your piston cylinder and increase the end and sample loads in increments, endload first then sample.

• Pressurize slowly and carefully. Each time you close the sample ram valve, pump a little to increase the pressure in the hydraulic line before slowly opening the endload valve, so that fluid is always bleeds in to the cylinder and pressure increases as the valve is opened. The target pressure should include a correction for friction.

Starting the experiment

• Program the Eurotherm controller.
• Reset the over temperature/power off alarm
• Turn the heat switch on (make sure that OP is 0 before doing this).
• Turn the potentiometer to 0.40.
• Start the data logger: open Igor, select Logger>Initialise, check the experiment name and click the start button.
• Start the heating cycle by pressing the run button of the Eurotherm controller.

  * If anything goes wrong, turn the heater switch off and reset the controller by pressing up and down buttons together *

• While the temperature is rising, the sample (lower) ram pressure will drop. Bleed hydraulic fluid in from time to time in order to maintain the desired pressure
• After reaching the set temperature, the sample (lower) ram pressure should be maintained. Increase pressure in if it is below the desired value, but do not depressurize if the pressure is too high.
• Close the main valve of your piston cylinder between pressure adjustments, and always check that the main valve of the other piston cylinder is closed before making adjustments to your experiment.
• Make plentiful notes in the lab book!

Quenching the experiment

• Press the up and down arrow keys on the front panel of the Eurotherm controller together. Immediately turn the potentiometer back to 0 and the heat off.
• When the thermocouple reads room temperature click the stop button on the data logger.
• Close the water in and water out valves to stop the flow of water to the apparatus.
• To drain water from the system, first open the drain valve, then slowly open the air valve so that the water is flushed through the system and into the drain. Once all the water is evacuated, close the air valve and then close the drain valve. READ THIS!
• You've probably blown some of the water out of the trap, so add a little water to prevent noxious gases from seeping back through the sewer pipes.
• Remove the water hoses from the stack.
• Disconnect the power cable from the stack.
• Disconnect the thermocouple.

Reducing the pressure

• The upper and lower ram valves should be closed at this point.
• Open the valve of the electric pump.
• Very carefully apply some torque to open the sample (lower) ram valve, so that the pressure slowly decreases. Do this as gently as possible - be patient.
• As the sample pressure decreases you may start to drain off some of the endload, but be sure to do this carefully. Sample load must always be decreased before endload.
• When the pressure is reduced and the hydraulic cylinders start to retract you can disassemble the stack.
• After removing the slotted plate, break the thermocouple insulator and cut the thermocouple wires. Return the thermocouple spool to its home.
• Remove the thermocouple plate. Wipe it dry and clean it.
• Remove the pressure plate. Cut the thermocouple wire that is sticking out of the base plug, and clean the surface of any thermocouple debris.
• Dry and clean the bridge.
• The cell assembly and the piston should be pushed out of the pressure plate using the 10 ton press. Before pushing out make sure that the push pin is properly aligned with the base plug. The push pin MUST NOT OVERLAP any part of the core.
• Close the shield and push out the assembly.
• Clean the pressure plate, check for cracks, and make notes of the observation. Spray the pressure vessel with T9 and wipe it with a cloth to protect against corrosion.
• Clean the piston and return it to its home.
• Start another experiment.

To prime the pressure controller

• Make sure that no one else is going to use the hydraulic pumps to pressurise an experiment while the cylinder is retracting.
• Close B main and open A main.
• Close the valves to shut off the sample and end load (lower and upper) cylinders of PC A.
• Open the pressure controller valve.
• Open the valve of the electric pump.

  At this point, there should be an open path for the pressure controller to suck hydraulic fluid from the tank of the hydraulic pump...

• Switch the pressure controller to manual, and reverse.
• Wait for the cylinder to retract fully. The motor will stop running when the limit switch engages; at this point the controller is primed and ready for use.

When you train someone to use the piston cylinder, read this document and update any part of the procedure as required.

ACW 2005

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