IMPULSE PIPPING

 Impulse piping is the piping (or tube) connection between a differential pressure gauge (or transmitter) and a differential head flow element (orifice plate, venturi tube, pitot tube etc.). 


 Impulse Piping Installation:



 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 piping, or the drain of a gas-filled impulse piping becomes plugged, the impulse piping 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 the transmitter.

Connecting Impulse Piping to the Transmitter (1) Check the High and Low Pressure Connections on the Transmitter (Figure 4.1) Symbols “H” and “L” are shown on a capsule assembly to indicate high and low pressure side. Connect the impulse piping to the “H” side, and the low impulse piping to the “L” side.

Routing the Impulse Piping 

(1) Process Pressure Tap Angles If condensate, gas, sediment or other extraneous material in the process piping gets into the impulse piping, pressure measurement errors may result. To prevent such problems, the process pressure taps must be angled as shown in Figure 4.5 according to the kind of

 fluid being measured

• If the process fluid is a gas, the taps must be vertical or within 45° either side of vertical. 

• If the process fluid is a liquid, the taps must be horizontal or below horizontal, but not more than 45° below horizontal.

 • If the process fluid is steam or other condensing vapor, the taps must be horizontal or above horizontal, but not more than 45° above horizontal.

Impulse Piping Connection Examples

 Figure 4.6, 4.7, and 4.8 shows examples of typical impulse piping connections. Before connecting the transmitter to the process, study the transmitter installation location, the process piping layout, and the characteristics of the process fluid (corrosiveness , toxicity, flammability, etc.), in order to make appropriate changes and additions to the connection configurations. 

Note the following points when referring to these piping examples. 

• If the impulse piping is long, bracing or supports should be provided to prevent vibration. 

• The impulse piping material used must be compatible with the process pressure, temperature, and other conditions.

 • A variety of process pressure tap valves (main valves) are available according to the type of connection (flanged, screwed, welded), construction (globe, gate, or ball valve), temperature and pressure. Select the type of valve most appropriate for the application.

 Routing the Process Piping

 (1) Relationship between Process Fluid and Manifold Locations (For the vertical impulse piping type) If condensate (or gas) generated in the process piping were allowed to accumulate, then it would be necessary to remove it periodically by opening the drain (or vent) plug. However, this would generate a transient disturbance in the pressure measurement. Therefore, the process piping must be routed so that any condensate (or gas) generated in the process piping will not accumulate in the pressure-sensing assembly of the transmitter.

• If the process fluid is a gas, then as a rule the manifold must be located at the downside of the pressure-sensing assembly.

 • If the process fluid is a liquid, then as a rule the manifold must be located at the upside of the pressure-sensing assembly.

 (2) Pipe Size for Process Piping Use a 15 mm (1/2-inch) pipe for process piping connection to the process connector. 

(3) Preventing Freezing If there is any risk that the process fluid in the transmitter pressure-sensing assembly could freeze, use a steam jacket or heater to maintain the temperature of the fluid.

 (4) Process Piping Connection Examples Figure 4.10 shows examples of typical process piping connections. Before connecting the transmitter to the process, study the transmitter installation location, the process piping layout, and the characteristics of the process fluid (corrosiveness, toxicity, flammability, etc.), in order to make appropriate changes and additions to the connection 

configurations. 

Note the following points when referring to these piping examples.

 • The process piping material used must be compatible with the process pressure, temperature, and other conditions.

 • A variety of process piping-mounted stop valves are available according to the type of connection (flanged, screwed, welded), construction (globe, gate, or ball valve), temperature and pressure. Select the type of valve most appropriate for the application.