Instrument Maintenance

Daily testing and cleaning

For safe use and long instrument life, keep the instrument


The instructions for operating the instrument should be followed carefully. The safety valve, in particular, should be tested each time the instrument is used. If the safety valve leaks or if it does not operate at pressures below 2 bar see Preparing the instrument and lubrication does not solve the problem, flushing the piston cavity with a solvent such as alcohol may help, especially if dirt or debris has entered the safety valve.

Dirt is the most common cause of instrument malfunction. Measuring plants with a pressure chamber almost always exposes the instrument to dirt and debris, so regular cleaning is essential. Periodic – at least once a day – removal of loose material in the chamber will reduce chances of scratching the ball valve packing of the Control Valve (causing leaks) or of plugging the tubing (rendering the instrument inoperative). After cleaning the chamber, add some petroleum jelly to the large O-ring in the cover. If the O-ring is particularly dirty, remove it with a small screwdriver (be careful not to scratch the O-ring groove!) or wooden stick, wipe it and the groove clean, apply fresh petroleum jelly to the O-ring, and reinstall it on the insert. Storing the instrument in a clean and lubricated condition helps prevent the O-ring from setting up, which makes the cover difficult to move.

Monthly cleaning and checking

During periods of continuous or hard use the instrument should be cleaned thoroughly at least once each month. Clean the chamber, cover, panel, and gauge with a strong liquid detergent cleanser. Remove the four screws which secure the outer edges of the panel and remove the instrument from the case. Clean any debris from the case. Place the instrument upside-down on a flat surface and inspect it for loose parts. Screws and fittings sometimes become loose if the instrument has been subjected to vibration such as might happen during transport in a vehicle. Tighten any loose fittings, but do not attempt to tighten fittings which aren’t loose. Over-tightening tube fittings can cause them to leak or fail. Inspect the hose for kinks or wear and replace it if it is cracked or worn. Remove the muffler (a filter looking device beside the valve assembly) and empty any dirt or debris which may have accumulated. Dirt in the muffler is an indication that the instrument has not been kept clean. Replace the muffler (no sealing tape is required for this fitting) and reinstall the panel in the case. Lubricate the O-ring and test the instrument following instructions under the section Preparing the Instrument.

Annual maintenance

At least once each year a thorough inspection of the instrument should be conducted. This inspection and cleaning is like the monthly cleaning and checking except that it should be more thorough. The instrument should be checked for leaks even though a leak is not suspected. The cleaning and inspection should include the removal of the insert from the cover and re-lubrication of the four small O-rings under the insert. After five years these O-rings may need replacing. The large O-ring seldom needs to be replaced. After the annual cleaning and maintenance the instrument should function as new. PMS Instrument also offers a annual cleaning, calibration and check-up service. Contact us directly if you are interested in this service.


Occasionally an instrument may develop a leak. If a leak is suspected, adjust the control valve as described below. If leak persists, conduct the following test: with the instrument out of the case, install a solid rubber gasket in the cover, pressurize the chamber to about 20 bar, then turn the control valve to OFF. Let the pressure stabilize for about one minute, then read the gauge. Wait ten minutes and read the gauge again. If the pressure decreased by more than 1 bar, locate the leak and repair it. A leak can usually be heard, but a soap solution applied to suspected fittings may help locate the leak precisely. If a fitting leaks, tighten it only enough to stop the leak. Over-tightening fittings will cause them to leak or fail. If a leak cannot be easily repaired, return the instrument to PMS Instrument Company for repair.

Adjusting the Control Valve