Permanent Pressure Loss for Primary Flow Elements

1. Purpose

This procedure defines the typical permanent pressure loss for various types of primary flow elements.

2. General

Hydraulic Tabulations must reflect the correct permanent pressure losses for primary flow elements for accuracy and proper specification of instruments. In most cases, standard orifice type flow meters are used, and the hydraulic program calculates the permanent pressure loss. However, orifice meters in special services and other types of flow meters may require assignment of different permanent pressure losses at normal flow rates. Note that normal flow rate means at 100 percent heat and weight balance flow rates.

3. Inflection Point Engineering Practices

Typical permanent pressure losses for primary flow elements at 100 percent heat and weight balance flow rates are shown in Appendix 1. Permanent pressure losses at flow rates other than 100 percent heat and weight balance flow rates are proportional to the square of the flow rate, as follows:

where subscript HWB refers to the 100 percent heat and weight balance flow rate, and subscript NEW refers to another flow rate.

Special considerations may be necessary for flow elements with wide variations in flow, very low pressure drop services, revamps, etc. Bring these exceptions, and primary elements not shown in the table, to the attention of the Process Control & Instrumentation personnel in the .

APPENDIX 1

Typical Permanent Pressure Losses for Primary Elements

1 Includes condensate return from steam heating exchangers and other bubble point liquids, such as from separators and column bottoms, piped directly to the orifice without intermediate coolers or pumps.

2 A strainer is required for Turbine, Positive Displacement and Rotameter.

3 Magnetic flowmeters are not differential-producing flowmeters but are included for completeness in this table.

4 The pressure loss indicated is a rounded value. Actual operating pressure loss will generally be lower.