How to increase the valve pressure difference ΔP (at full close) parameter of the control valve

Isn’t it just the maximum difference in pressure before and after the valve? Right? Why is it necessary to consider the pressure difference? It is mainly to select the appropriate actuator based on the pressure difference and diameter, so as to ensure that it can operate under the maximum pressure difference while meeting the desired leakage level.

For example, in this scenario, a water pump has a head of 100 meters, and the water pressure before the pump is 0.3 MPa. There is a control valve behind the pump; assuming that the pump, the valve, and the equipment inlet are at the same height, the normal operating pressure of the equipment behind the valve is 0.6 MPa. Now, we need to purchase this control valve – what are the pressures before the valve, after the valve, and the pressure difference across the valve?

This post was last edited by bfdlwolf on 2019-11-18 09:19. ‘Guidelines for the Selection of Pipe Sizes in Petrochemical Process Units’ (SH/T 3035-2018), 6.1.5: The pressure drop of control valves should be determined based on the process operating conditions and the characteristics of those valves. Under normal flow conditions, the pressure drop across the control valve should not be less than 30% of the pressure drop in the pipeline system; in pipeline systems with relatively stable flow, it can be set at no less than 20% of the pipeline system’s pressure drop. Explanation of clause 6.1.5: In pipeline systems, the pressure drop required by control valves must be taken into account; otherwise, the control valves cannot function properly. The pressure drop required for a control valve is related to the type of control valve, the pressure drop in the pipes and equipment at normal flow rates, as well as the range of flow variations. Chapter 5 of \"Chemical Engineering Volume VI: Introduction to Chemical Plant Design\" (by J. M. Coulson and J. F. Lijason) states: \"The pressure drop required by a control valve varies depending on the design of the valve. When selecting the specifications for a pump, it is necessary to ensure that there is sufficient pressure drop to allow the control valve to function properly across the entire desired flow range. If possible, the control valve and the pump should be considered as a single unit, with their sizes determined together so that the optimal specifications for both can be selected.\" As a general guideline, if certain characteristics are not specified, the pressure drop across the control valve should be at least 30% of the total dynamic pressure drop in the system; the minimum value for this pressure drop is 50 kPa. The main factor affecting the pressure drop required for the control valve is the range of flow variations. Therefore, these guidelines specify a slightly lower value for pipeline systems with more stable flow rates, in order to reduce the energy consumed by the control valves. The pressure drop in the pipeline here refers to the pressure drop associated with flow rate, including the resistance losses incurred while fluid flows through pipelines, heat exchangers, mixers, nozzles, valves, and pipeline fittings; it does not include back pressure or head differences.

The valve pressure difference ΔP (at full closure) is relevant to the selection of the actuator as well as the safety factor.