A primary pressure regulating valve is a valve that keeps the pressure on the valve’s inlet side (primary side) at a set value. Even when the upstream supply pressure fluctuates, once the primary side exceeds the set pressure the valve opens to release the excess pressure, suppressing pressure spikes flowing into the equipment. Its control target is the opposite of a pressure reducing valve, which keeps the secondary side constant; the two are used according to whether “what you want to protect is the equipment’s inlet pressure or its outlet pressure.” It is used in systems where the supply pressure tends to move, such as pump discharge or steam headers, when you want to protect downstream equipment from overpressure and stabilize the pressure.
Key points of this article
- A primary pressure regulating valve keeps the “primary side (inlet) pressure” at a set value and releases the excess to protect downstream equipment.
- Its role is the reverse of a pressure reducing valve, which keeps the secondary side constant, and it is suited to protecting and stabilizing systems where the supply pressure fluctuates.
- For selection, the basic approach is to check the fluid, set pressure, maximum/minimum flow rate, connection bore, and allowable pressure range for each set of conditions.
How a primary pressure regulating valve works and its role
Action that keeps the primary side pressure constant
A primary pressure regulating valve consists of a valve disc, a spring (or setting mechanism), and a diaphragm, and it detects the primary side pressure to adjust the valve opening. When the primary side rises above the set pressure, the valve opens and releases the excess fluid to the secondary side, suppressing the rise on the primary side. Conversely, when the primary side falls, the valve moves toward closing and tries to maintain a certain level of pressure on the primary side. As a result, fluctuations in the upstream pump or steam supply are less likely to be transmitted directly downstream.
Difference from a pressure reducing valve
The pressure reducing valve is easily confused with it, but the side being controlled is different. A pressure reducing valve keeps the secondary side (outlet) pressure constant, whereas a primary pressure regulating valve keeps the primary side (inlet) pressure constant. Therefore, when you “want to stabilize the pressure sent out to the equipment,” a pressure reducing valve is the candidate, and when you “want to keep the pressure of upstream equipment or a header constant and release the surplus,” a primary pressure regulating valve is the candidate. Its role also differs from a protective device such as a safety valve, which operates only under abnormal conditions; the primary pressure regulating valve is characterized by continuously adjusting pressure during operation.
The idea of protecting equipment from supply pressure fluctuations
There is not necessarily only one cause of supply pressure fluctuation; multiple factors are involved, such as the pump’s operating status, simultaneous use of multiple pieces of equipment, load variation, and piping resistance. In such systems, installing a primary pressure regulating valve on the primary side can, in some cases, ease momentary pressure spikes and reduce the burden on downstream valves, instruments, heat exchangers, and the like. However, separate measures may be needed for steep surges or water hammer, and a primary pressure regulating valve alone cannot prevent all pressure abnormalities.
Criteria to check for selection and installation
Pin down the conditions for fluid, set pressure, and flow rate
At the time of selection, organize the type of fluid (water, steam, air, oil, etc.), temperature, the primary pressure you want to set, the anticipated maximum and minimum flow rates, and the connection bore for each set of conditions. In particular, flow rate matters not only at its maximum value but also at its minimum value; if the flow rate is smaller than expected, control may become unstable. The figures are only a guide, and the appropriate size will change depending on the actual operating conditions.
Points to note for installation
It is advisable to secure a straight pipe section before and after the valve for flow conditioning, and to install it at a position where pressure can be detected correctly. Also, since jamming by debris or scale is a cause of malfunction, consider installing a strainer on the upstream side. With maintainability in mind, it is reassuring to also check the space needed for inspection, cleaning, and parts replacement, as well as whether a bypass line is required.
Frequently asked questions
Q1. Should I choose a primary pressure regulating valve or a pressure reducing valve?
A1. Decide based on whether the pressure you want to protect is on the inlet side or the outlet side. As a basic way of thinking, if you want to keep the inlet (primary side) constant, choose a primary pressure regulating valve; if you want to keep the outlet (secondary side) constant, choose a pressure reducing valve.
Q2. If I have a safety valve, is a primary pressure regulating valve unnecessary?
A2. Their roles differ. A safety valve is a device that opens under abnormal conditions to protect equipment, while a primary pressure regulating valve is a valve that continuously adjusts pressure during operation. They may also be used together depending on the purpose.
Q3. To what extent can supply pressure fluctuations be absorbed?
A3. It varies depending on the valve specifications and flow conditions, so it cannot be stated in general terms. Separate measures may be needed for steep surges or water hammer, so please provide your conditions and consult with us.
Q4. Is it fine to match the bore to the piping size?
A4. The piping bore and the valve’s appropriate bore do not necessarily match. The basic approach is to select based on flow rate and set pressure; simply matching it to the pipe diameter can make control unstable.
Q5. Can it be used with steam?
A5. You need to select a specification suited to the fluid and temperature. For steam applications, conditions such as materials, seals, and drain measures are added, so we check the model based on the conditions of use.
Q6. I would like to replace an existing valve with an equivalent product.
A6. Even if the model or specifications are unknown, if the fluid, bore, set pressure, and conditions of use are known, they can serve as a guide for selection. If you provide the nameplate information and installation situation, we can consider it more accurately.
Summary and please consult us
A primary pressure regulating valve is a valve that keeps the primary side pressure constant in systems where the supply pressure fluctuates, protecting downstream equipment from overpressure. Because its role differs from that of a pressure reducing valve or a safety valve, the first step in selection is to start from “whether you are protecting the inlet side or the outlet side.”
“I cannot judge whether the valve bore is appropriate for the piping bore,” “I know the maximum flow rate but not the minimum flow rate,” “The supply pressure fluctuation range is large and I am unsure which model to select,” “I want to select an equivalent product for an existing valve”—if you have such specific concerns, please make use of Yoshitake’s technical and selection consultation. If you let us know the fluid, bore, set pressure, conditions of use, and so on, we can propose a selection tailored to your conditions.