【Discussion】Method for setting the output pressure of a self-acting control valve.
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The last edit to this post was made by xzzgjxmf on 2017-7-22 at 13:54. As the title suggests, it concerns whether the output pressure is adjusted dynamically (by opening a manual valve to apply pressure to the container) or statically (with the manual valve fully closed after the self-acting valve to establish backpressure).
It is best to adjust the back pressure to zero first (it is necessary to know the multiplicative relationship between the shutdown pressure and the pressure under dynamic operation), then open the valve to start operation; if the pressure does not meet the requirements, further fine adjustments can be made.
The purpose of using a self-acting control valve is to automatically adjust the pressure that needs to be controlled in a process, without the need for manual adjustment. If the manual valve is closed completely, then it loses its meaning; the adjustment should be made while the process is operating normally, in order to find an appropriate set pressure. Before the valve is put into use, it can be set to the designed pressure, and if the adjustment effect is not satisfactory, further fine-tuning can be carried out
In principle, self-acting valves do not require adjustment or calibration after leaving the factory; their accuracy of adjustment is poor, and there are significant errors in the set pressure values. As can be seen from the diagram, there should be a local pressure gauge behind the valve. If the valve adjustment error is too large, fine-tuning should be carried out using the local pressure gauge behind the valve; it is best to issue an order to have the process engineers come to the site.
This post was last edited by cqdfwy on 2017-8-3 at 11:58. The adjustment of pressure for a self-acting control valve here refers to the preparatory steps taken before it is put into operation (it’s similar to when changing the setting of a regulator: one must always switch it to manual mode in order to adjust the setting, as doing so directly in automatic mode will cause fluctuations). If the control requirements are not high (the downstream equipment has modest demands regarding medium flow rate, pressure stability, and pressure control), and the pressure difference upstream and downstream of the self-acting control valve is not significant, it is feasible to set a pressure value while the system is in operation ； If high control requirements exist, especially when the pressure difference upstream and downstream of the self-acting control valve is significant, setting a pressure value while the system is in operation will inevitably cause substantial changes in the flow rate of the medium and the pressure downstream, which in turn can affect the stable operation of the equipment downstream. Therefore, it is more reasonable to use the manual valve to reduce the pressure in such situations.