(a) Pulsation Dampeners. Dampeners may be included in sensing take-off lines and are available in stainless-steel construction in %-in. and V2-in. pipe sizes. (In Fig. 4.22 item 14 is a typical pressure dampener.) One design consists
of a sintered stainless-steel disk or cylinder held in a stainless-steel body; another a captive stainless-steel pin in an orifice opening. Plugging may present a problem; so periodic cleaning may be required. Some sensors have electronic dampening of the output signal to avoid a mechanical dampener.

(b) Diaphragm Seals. Stainless-steel diaphragm seals can be used when a sensor is not corrosion resistant or is subject to possible contamination. The space between the sealing diaphragm and the sensor is filled with a suitable liquid whose pressure duplicates that on the process side of the diaphragm. Fluids satisfactory for temperatures up to 350°F service are common. The seals are usually assembled m the factory to ensure a complete fill. Diaphragm seals are commonly used on Bourdon tubes and in force-balance capsules involving minimum displaced volume. Excessive displacement may involve an error arising when the spring rate of the seal diaphragm is added to the measured pressure. A seal diaphragm is part of the design in F’ig. 4.17.

(c) Overpressure Devices. Pressures in excess of the normal design rating of the sensor may be encountered. For such emergencies a self-operating shut-off valve may be installed between the take-off and the sensor and set to close at preset point to protect the sensor. Stainless-steel guards are available in У4-іп. and У2-іп. pipe sizes for operation up to 9000 psi.

(d) Siphons. Siphons or loops in take-off piping are used to keep hot fluids from contacting the sensor mechanism, which has usually been calibrated at ambient. Performance tests on the sensor indicate the maximum temperature that can be tolerated. The strain-gage sensor in Fig. 4.17 includes coolant connections.