The pressure vessel is made of stainless steel material which resists high pressure (40 bars or 600 psi). The pressure vessel may be of different sizes, such as the pressure vessel of pressure bomb model 3000, which is 2.75" x 6.5" deep. With these dimensions, it is possible to measure a wide variety of sample sizes (large leaf, stem, branch or a small plant).
The pressure vessel has four internal cams at the vessel top which help to hold the specimen holder during the performance of each run. High gas pressure is applied in the center of the vessel in the point where the sample was placed. After reading and exhausting the pressure, the specimen holder is placed away from the pressure vessel by turning the top cap counterclockwise 45º, and then taking out the holder vertically. For the next sample run, the holder with the sample is placed in the vessel in the same opposite way (like it was removed) as described above. The specimen holder components are: sealing knob, closing ring, support washer, sealing plug, and housing.
All pressure bombs need nitrogen gas as a source of pressure for plant moisture stress (PMS) measurements in plant tissue. Nitrogen gas can be supplied from a big supply tank which is directly connected to the console. This is commonly used when measurements are carried out in the laboratory, close to the field. On the other hand, nitrogen can also be supplied from the storage tank (refillable, 2000 psi, 25 cu. ft. capacity) held beneath the chassis of the console. When empty, the compressed gas cylinder can be refilled with or without removing it from the chassis. When not using the console, the sealing valve at the upper end of the storage tank, should be kept closed (turned clockwise).
The preparation board is useful and practical for sampling preparation. The specimen holder is placed over the preparation board in horizontal position, the old sample is removed and the new sample is placed in the specimen holder for the next reading.
pressure source regulator
Only the console model 3005 has the pressure source regulator, which is linked to the compressed gas tank. This source regulator is taken away when the gas cylinder is replaced or refilled. Regularly, for standard consoles, the pressure on the regulator has been set at the factory at 600 psi. One of the parts of the pressure source regulator has a screwed pressure gauge and directly shows the pressure within the gas tank, which in turn can be a sign of gas depletion and the need of nitrogen refillment.
The metering valve is a device that regulates and measures the flow of the gas from the compressed gas cylinder to the pressure vessel. This valve is designed with a fine adjustment which allows a careful control in the pressure rate within the pressure vessel. In order to get the highest quality in making measurements, the metering valve has to be gradually operated in a increasing pressure rate ranking from 5-10 psi/sec.
The three way control valve as its name implies, has three different positions which are "OFF", "PRESSURIZE" and "EXHAUST". The "OFF" position indicates that there is not gas pressure into the pressure vessel because the flow of gas is sealed. The "PRESSURE" position indicates that the gas is flowing from the compressed gas cylinder into the pressure vessel. Finally, the "EXHAUST" position means that high pressure gas is released from the pressure vessel to the atmosphere.
The gauge is a manometer which allows one to read the pressure in the tank when a sample is evaluated. The gauge can be fixed on the console or adjustable according to the model.The gauge is graduated in bars , PSI (lb/Inch2), pascal or Megapascals, with minimal graduation of 2/10 bars.The gauge has a zero adjusting screw which allows one to set up the pointer in the zero position if it is necessary, specially after transporting the instrument. To adjust the zero position, the cover glass must be removed, turning the cover plate counterclockwise. The zero adjustment screw is located close to the bottom of the gauge. There is another mechanism to zero adjustment. This is a friction type adjustable pointer. In this case, the pointer must be moved until the zero position holding the knurled disc, which is located in the center of the pointer.