Impulse Piping For Absolute And Differential Models - Siemens 7MF4333 User Manual

Installation

4.3.3 Impulse Piping for Absolute and Differential Models

Impulse piping is the piping to be connected to the transmitter's process connection(s). For suggested
flow and level measurement piping arrangements, refer to:
•
Differential Model - Figures 4-1 and 4-2
•
Absolute Model - Figures 4-3 and 4-4
•
Flange Model - Figure 4-5
Note the following when planning and installing piping.
•
Install impulse piping in accordance with ANSI Code B31.1.0.
•
Make impulse piping length as short as possible to reduce frictional loss and temperature-induced
pressure variations.
When using impulse lines on a high temperature process, locate the transmitter far
enough away from the heat source to keep it within temperature specifications [28°C
(50ºF) per foot cooling to a normal ambient is assumed for non-insulated impulse lines].
•
For lines between the process and transmitter, use impulse piping of 3/8" OD or larger to avoid
friction effects (causes lagging) and blockage.
•
Use the least number of fittings and valves possible to minimize leakage problems. Teflon
recommended thread sealant for process connections at the transmitter.
•
Valves used in pressure service should be either globe or gate type. Valves used in gas service should
be of a type that does not permit condensate to build up behind the valve.
•
Install sediment chambers with drain valves to collect solids suspended in process liquids or moisture
carried with non-condensing gases.
•
Install air chambers with vent valves at high point in piping to vent gas entrained in process liquid.
•
Remote diaphragm seals can be used to keep corrosive liquid or gas from the transmitter pressure
inlets and isolation diaphragm.
•
Alternatively, use sealing fluid to isolate the process from the transmitter. Sealing fluid must be of
greater density than process fluid and non-miscible.
•
For transmitters located above the process, slope piping from the transmitter at least 1 inch/foot (83
mm/M) down toward process. For transmitters below the process, slope piping at least 1 inch/foot (83
mm/M) up to process.
•
Protect pressure lines (by shielding if necessary) from objects or equipment that may bend or kink the
line causing fluid flow restriction.
•
Protect the pressure lines from extreme temperature ranges. Lines should be protected from freezing
by installing a heat trace.
•
A three-valve manifold should be used with a differential transmitter model. A two-valve manifold
can be used with an absolute model to permit servicing and zero checks.
4-4
IMPORTANT
UMSITRPDS3-1
®
tape is the
November 2010