Pressure measurement is a critical function in Process Control. It is measured locally or via a pressure transmitter. Pressure guage is used to read the system pressure locally.
Pressure transmitter is used to send pressure singnal to DCS for further processing and action. Usually, a 3/4″ branch connection (threaded or flanged) along with a block valve such as gate valve is used to connect pressure sensor to the piping system. On equipments, flanged pressure sensor is directly installed on designated nozzle. Local pressure gauge dial can be of fixed orientation or with a swivel head so that it can be turned for comfortable viewing angle.
Pressure sensor branch should be located at least 6 pipe diameters form pressure fluctuating situations like pipe branch, control valve etc. Both a local sensor and a transmitter can be located on the same branch from main pipe.
Pressure guage near grade should be readable without a portable ladder. Pressure on platforms should be at least readable from a fixed ladder. Pressure gauges in piping systems at such equipments as pump discharge lines must be located as close to the equipment as possible.
Pressure sensor should be located in vapor space on a Distillation Tower. Instrument hookup drawing should be referred while modelling Pressure instrument on a pipe or equipment.
Piping Layout Considerations
Local pressure indicators shall be visible from grade, permanent ladder or platform. Those located less than 4500 mm above high point of finish surface and in a pipeway shall be accessible by portable ladder.