Installation location of the manual control valve?
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I recently encountered a challenge in design: should manual control valves be used in the supply pipeline or the return pipeline? It was previously used in return water pipes, and many documents also state this ； But now the manager suddenly wants it installed on the water supply pipeline. The manager said that if it’s installed on the return pipeline, larger pumps will have difficulty starting and cavitation is likely to occur. This post was last edited by skybiue123 on 2009-3-31 15:10.]
To prevent cavitation, in closed systems, it is better to install it on the water supply pipeline; in our actual installations, we have not yet seen it installed for adjustment before the pump；
1. A valve is defined as a device in a fluid system used to control the direction, pressure, and flow rate of the fluid. A valve is a device that allows or stops the flow of media (liquids, gases, powders) within pipes and equipment, and can also control its flow rate. 2. Manual control valves use manual effort to adjust the flow rate of the fluid in the system. 3. In a heating network system, if there is only one main pipeline without any branch pipelines, then it is not necessary to install control valves ； Only when there are two or more branch pipelines in the system, and in order to maintain hydraulic balance in the piping network, are manual control valves installed on the supply or return water lines of each branch. 4. “Adjustment” – as the name implies, it involves making adjustments in quantity or degree to meet the requirements ； In other words, the flow rate in each branch pipeline needs to be adjusted to the optimal required level, rather than reducing the total flow rate required by the system. Therefore, whether the control valve is installed on the supply or return pipeline, as long as the total flow rate of the system is not less than the flow rate specified on the water pump’s nameplate, there is no such thing as a \"cavitation\" problem. Conversely, if the control valve is installed on the system’s water supply pipeline, what consequences will arise if the total flow rate is lower than the flow rate specified by the pump’s nameplate? 5. As the moderator mentioned, “It has always been used in return water pipes, and many documents also state this.” Indeed, the author has been working in the HVAC field for many years, having installed, managed, and tested numerous heating systems; control valves are always installed on the return water pipes of the branch systems. I have never seen the phenomenon of water pumps being difficult to start or suffering from cavitation. 6. In heating systems, improper selection of the circulation water pump – such as an excessively high head – results in the pump’s performance curve not matching that of the actual pipeline system. This leads to excessive flow rates in the pump and excessive current in the motor, preventing the pump from operating properly. At this time, the valve at the outlet end of the water pump can be used as a regulating valve; closing it slightly can ensure the normal operation of the circulation water pump. The above points are my immature opinions; please feel free to correct any mistakes, moderators, so that we can discuss them together.
In fact, what my six points above aim to convey is this: the key to installing a control valve lies in determining which flow rate needs to be regulated. If the goal is simply to adjust the characteristic curve of the water pump, then the valve must be installed on the outlet pipe of the pump; installing it at the inlet pipe of the pump will inevitably increase the vacuum level within the pump, leading to \"cavitation\". For the entire hot water heating network system, it can be installed on both the supply and return pipes without any problem.