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Since 1962

CATALOG 2000

Operating Instructions

LIQUID FILLING -  When a Zeal is attached to a pressure instrument, the two must act as an integral unit.  To accomplish this, all the cavities, or space, occupied by air in the instrument flange of the Zeal, in the sensing element of the pressure instrument and in the hole through the capillary tubing (if used) must be filled with a fluid.

Liquid Filling Installation Maintenance Diaphragm Replacement

The function of the liquid fill fluid is to transmit the process pressure, which acts on the diaphragm, from the diaphragm to the sensing element of the pressure instrument.

Usually, this fluid is a light instrument oil but other fluids can be used should oil tend to contaminate the process in case of leakage.

The instrument/seal assembly can be filled in either of two methods.

The instrument and seal can be filled separately and then assembled.  Back pressure, if present, should be relieved by use of the fill/bleed screw provided in the seal for this purpose.

The liquid filling operation can be done by evacuating all the air from all the cavities in the pressure instrument with the aid of a vacuum pump and then, by the proper arrangement of pipes and valves, allowing the fill fluid to replace the evacuated air in the cavities.  The cavity in the instrument flange of the diaphragm seal can be easily filled through the instrument connection from an oil can or other container prior to attaching it to the pressure instrument.

In the second method of filling, the instrument and seal are assembled first, then the entire internal cavities of the instrument and seal can be evacuated and completely filled through the fill/bleed port by the use of a fill adapter that is inserted into the port.  After filling, the bleed screw is inserted into the fill/bleed port to seal it.  If you use this method, it is strongly recommended that an equal vacuum be pulled on the process side of the diaphragm, especially on the Type T and Type V Zeals.

It is a fact that the smallest amount of movement, required of the diaphragm, occurs when all the air is removed from the unit.

It is also a fact that the larger the amount of movement required to fully actuate a sensing element of a pressure instrument, the greater the spring rate of a diaphragm.  The greater the spring rate - the greater the inaccuracy of the unit.  These facts are inherent regardless of make or manufacturer of the diaphragm seal.

The spring rate of the diaphragm can be calibrated into the assembled unit by recalibrating the unit after liquid filling.  But, this is possible only if the calibration range of the sensing element in the pressure instrument is great enough to compensate for the added spring rate of the diaphragm.  In instruments of low pressure range, the spring rate of the sensing element is too small to allow for the compensation necessary for the high spring rate of some diaphragms.  In fact, the spring rate of some diaphragms is so great that it is equal to and sometimes even greater than the spring rate of the sensing element in low pressure instruments.

The more precise and exacting the process requirements, the more important it is to remove all the air from a pressure instrument and to carefully recalibrate the unit after liquid filling.

In the large Type T Zavoda Diaphragm Seal (Zeal), the spring rate of the diaphragm is equal to only two ounces of pressure per square inch, when all the air is evacuated from the unit, and is so small that in most uses this will not require the costly recalibration of the instrument. 

INSTALLATION - Depending on model used, Zeals can be welded, bolted or threaded into the process system using any good installation procedure.  A hole is provided in the instrument flange for the use of a pin spanner wrench when attaching a Zeal onto a threaded process pipe. 

MAINTENANCE - All Zeals in all series, except styles 10 and 11, are of the cleanout type and, by removing the flange bolts, can be separated at the flanges without loss of the liquid fill fluid to permit periodic cleaning of the diaphragm.

The cavity in the process flange and the process side of the diaphragm must be kept clean and free of any clogging matter, otherwise proper movement of the diaphragm may be impaired.

The retention of the liquid fill is accomplished by the diaphragm being firmly held by a holding groove in the instrument flange. 

CAUTION - At all times extreme care must be taken not to nick or scratch the gasketing surfaces or leakage may result.

DIAPHRAGM REPLACEMENT - When removing a damaged diaphragm from the instrument flange, extreme care must be taken not to dent, nick or otherwise damage the groove are at the instrument flange gasketing surface face.

Install a new diaphragm by inserting one point of the diaphragm into the holding groove with the instrument flange gasket assembled in place on the diaphragm and then press the diaphragm in with the fingers pushing down on the thickened edge of the diaphragm and working around the periphery until the opposite side has been reached.

Lightly oil all parts to aid in installation, if necessary, but hammers or like objects should not be used, as they may dent or nick the gasketing surface and may result in leakage after assembling.

Zeals with the style numbers 10 and 11 do not have the holding groove in the instrument flange, nor the self-holding type of diaphragm.  Therefore, to assemble a diaphragm into one of these models, simply assemble an instrument flange gasket in place and insert the diaphragm into the recess provided for it in the instrument flange and bolt the process flange to the instrument flange.