For pressure sensing equipment, there are multiple accessories for optimal functioning in difficult process settings. Sometimes unique accessories must be used to safeguard the pressure tool from the risks of certain process liquids.
Bleed (vent) fittings
Pressure pulsation damping
The valve manifold includes manual valves for maintenance and calibration reasons to isolate and equalize pressure from the system to the transmitter. These device isolates the DP transmitter from the process, for maintenance and calibration process. Manifolds are combination of block valves and equalizing valves.
There are mainly two types of valve manifolds, 3 valve manifolds and 5 valve manifold.
Bleed (vent) fittings:
The engineer must “breathe” or “vent” accumulated liquid pressure to the environment before removing a pressure transmitter from live operation to attain a zero power state before disconnecting the transmitter from the impulse lines.
An inexpensive and common accessory for pressure-sensing instruments is the bleed valve fitting or vent valve fitting, installed on the instrument as a discrete device.
Pressure pulsation damping:
Filling the inside of the gage with a viscous liquid such as glycerin or oil is a easy way to mitigate the impacts of pulsation on a pressure gage. This filling liquid’s intrinsic friction has a “shock absorber” quality that dampens the oscillatory movement of the gauge mechanism and helps safeguard against harm from pulsation or internal vibration.
Remote and chemical seals:
Isolating diaphragms have merit even in scenarios where pressure pulsations are not a problem. Consider the case of a food-processing system where we must remotely measure pressure inside a mixing vessel.
Process pressure presses against this diaphragm, which in turn transfers pressure to the “fill fluid” inside the capillary tube. This sealed fill fluid then presses against the instrument’s sensing element (diaphragm, bourdon tube, bellows, etc.).
The picture above shows a pressure gage fitted with a diaphragm of a chemical seal. Note that the chemical seal on this specific gage is closely linked to the gage, since the only objective here is to protect the gage against difficult process liquids, not the capacity to mount the gage remotely.
The 2-inch pipe mounting bracket is an accessory specifically intended for a range of field-mounted tools including DP transmitters. Such a bracket is made of heavy-duty sheet metal and is fitted with a U-bolt intended to clamp around any black iron pipe of 2 inches.
Holes stamped in the bracket match mounting bolts on the capsule flanges of most common DP transmitters, providing a mechanically stable means of attaching a DP transmitter to a framework in a process area.
In installations where the ambient temperature may become very cold, a protective measure against fluid freezing inside a pressure transmitter is to house the transmitter in an insulated, heated enclosure. Which is shown below: