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Installation UMSITRPDS3-1

November 2010

4-4

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.

IMPORTANT

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

tape is the

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.

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Siemens SITRANS P Bedienungsanleitung Seite 56