Yokogawa EJX930A - Manual (Page 34)

<6. Installing Impulse Piping>
6-1
IM 01C25R01-01E
6. Installing Impulse Piping
6.1 Impulse Piping Installation
Precautions
The impulse piping that connects the process
outputs to the transmitter must convey the process
pressure accurately. If, for example, gas collects
in a liquid-filled impulse line, or the drain for a
gas-filled impulse line becomes plugged, it will
not convey the pressure accurately. Since this will
cause errors in the measurement output, select
the proper piping method for the process fluid
(gas, liquid, or steam). Pay careful attention to the
following points when routing the impulse piping
and connecting the impulse piping to a transmitter.
6.1.1 Connecting Impulse Piping to a
Transmitter
(1) Check the High and Low Pressure
Connections on the Transmitter (Figure 6.1)
Symbols “H” and “L” have been placed on the
capsule assembly to indicate high and low pressure
side. With differential pressure transmitters, connect
the high pressure side impulse line to the “H” side,
and the low pressure side impulse line to the “L”
side.
With gauge/absolute pressure transmitters, connect
the impulse line to the ‘H’ side.
F0601.ai
Process
connection
“H” and “L” are shown
Process connection
Process connector
Bolt
Differential Pressure Transmitter
Figure 6.1 “H” and “L” Symbols on a Capsule
Assembly
(2) Changing the Process Connector Piping
Connections (Figure 5.1)
The impulse piping connection distances can be
changed between 51 mm, 54 mm and 57 mm by
changing the orientation of the process connectors.
This is convenient for aligning an impulse line with a
process connectors.
(3) Tightening the Process Connector
Mounting Bolts
After connecting an impulse line, tighten the
process connector mounting bolts uniformly.
(4) Removing the Impulse Piping Connecting
Port Dustproof Cap
The impulse piping connecting port on the
transmitter is covered with a plastic cap to keep out
dust. This cap must be removed before connecting
the line. (Be careful not to damage the threads
when removing this cap. Never insert a screwdriver
or other tool between the cap and port threads to
remove the cap.)
(5) Connecting the Transmitter and 3-Valve
Manifold
A 3-valve manifold consists of two stop valves to
block process pressure and an equalizing valve
to equalize the pressures on the high and low
pressure sides of the transmitter. Such a manifold
makes it easier to disconnect the transmitter
from the impulse piping, and is convenient when
adjusting the transmitter zero point.
There are two 3-valve manifold types: the pipe-
mounting type and the direct-mounting type; care
should be taken with respect to the following points
when connecting the manifold to the transmitter.
 Pipe-Mounting Type 3-Valve Manifold
(Figure 6.2)
1) Screw nipples into the connection ports on the
transmitter side of the 3-valve manifold, and
into the impulse piping connecting ports on
the process connectors. (To maintain proper
sealing, wind sealing tape around the nipple
threads.)
2) Mount the 3-valve manifold on the 50 mm (2-
inch) pipe by fastening a U-bolt to its mounting
bracket. Tighten the U-bolt nuts only lightly at
this time.
3) Install the pipe assemblies between the 3-valve
manifold and the process connectors and lightly
tighten the ball head lock nuts. (The ball-shaped
ends of the pipes must be handled carefully,
since they will not seal properly if the ball
surface is scratched or otherwise damaged.)