A pressure control valve automatically keeps fluid pressure at a set level inside a system. You use these devices every day without noticing them. Think about your water heater at home. A relief valve protects it from dangerous overpressure that might cause an explosion. This small part always checks system pressure and opens when levels get too high.

Good pressure control protects equipment, boosts efficiency, and prevents accidents. Without proper regulation, pipes can burst, seals can break, and machinery can wear out early. You depend on these valves in many places, from home plumbing to huge industrial plants. Knowing how they work helps you see their key role in keeping systems safe and dependable every day.

Key Takeaways

• A pressure control valve keeps fluid pressure at a safe level in a system.

• It uses a spring and diaphragm to balance forces and keep the setpoint steady.

• Relief valves keep systems safe from too much pressure by opening up when the pressure gets dangerously high.

• Pressure reducing valves keep the pressure on the outlet side steady at a lower level.

• Sequence valves decide which part of a hydraulic system moves first.

• Pick the correct valve by checking pressure, flow, and the type of fluid.

• Installing it the right way and keeping up with maintenance stops breakdowns and lost time.

• Good pressure control makes many industries safer and more efficient.

What Is a Pressure Control Valve?

Definition and Purpose

A pressure control valve is a mechanical device that automatically keeps fluid pressure at a desired level inside a system. It opens or closes based on a setpoint that an engineer determines ahead of time. The valve uses a pressure transmitter to detect changes and sends signals to adjust the valve position. This process happens continuously to keep the system stable. You find these valves in many places, from home water heaters to large industrial plants.

Think of a pressure cooker on your stove. The regulator on top releases steam when pressure gets too high. It keeps the pressure inside the pot at a safe level for cooking. This valve works the same way in industrial systems. It monitors the pressure and adjusts the flow to maintain the right balance. When the system pressure rises above the setpoint, the valve opens to release fluid. When pressure drops below the setpoint, the valve closes to build pressure back up.

The precise engineering definition states:

The pressure control valve is used to regulate the pressure of a fluid passing through the pipe. It opens and closes based on a setpoint predetermined by an engineer, typically controlled using a pressure transmitter (PT) that sends signals to the valve to compensate for pressure variations.

Several industry standards classify and define these valves. These include IEC 60534-4, ANSI/FCI 70-2, API 598, ISO 5208, MSS SP-61, and NAMUR NE 107. These standards ensure consistent performance across different manufacturers. They also establish testing procedures that verify each valve meets its design specifications.

Key Role in System Safety

Pressure control and regulation is essential for safe system operation. When hydraulic pressure drops below the optimal range, the system cannot deliver the force it needs. This leads to reduced power, slower operation times, and decreased productivity. In critical applications, low pressure can compromise safety. For example, a hydraulic press may fail to form a part correctly if the pressure is too low.

Excessive pressure puts too much strain on the system. This increases the risk of leaks, component damage, and potential failures. These problems result in costly repairs and unexpected downtime. Maintaining the correct pressure balance prevents these efficiency losses and safety hazards. The valve acts as a safeguard that protects both the equipment and the people working nearby.

The consequences of poor pressure regulation vary by system type. Pneumatic systems operate at lower pressures and reduce the risk of catastrophic failures. However, the sudden release of compressed air can still cause injuries or propel debris at high velocities. Hydraulic systems operate at much higher pressures. They present greater risks of high-pressure fluid injection injuries and more severe consequences when components fail. A small leak in a hydraulic line can inject fluid into your skin, causing serious tissue damage.

Basic Components of a Pressure Control Valve

Every such valve has several key parts. The body houses the internal components and connects to the pipe system. It must withstand the maximum pressure the system can produce. The valve seat creates a seal when the valve closes. A worn seat can cause leakage even when the valve is fully shut. The plug or disc moves to open or close the flow path. Its position determines how much fluid passes through the valve.

The spring provides the opposing force that balances against the system pressure. Engineers select springs with specific stiffness ratings to match the desired setpoint range. When system pressure pushes against the spring, the valve opens or closes to maintain the setpoint. The diaphragm senses pressure changes and transmits this information to the valve mechanism. It acts as a sensor that converts pressure into mechanical motion. These components work together as a feedback loop to keep the system stable. The loop operates continuously, making small adjustments many times per second.

How Pressure Control Differs from Flow Control

Understanding the difference between pressure control and flow control helps you choose the right valve. In fluid power systems, these two types serve different purposes. Many people confuse them, but they control completely different aspects of the system.

A flow control valve regulates how much fluid moves through the system. It manages the rate of fluid movement to determine actuator speed. When you need a cylinder to extend at a certain speed, you use a flow control valve. It restricts the flow path to limit the volume passing through per unit of time.

A pressure control valve regulates how hard the fluid pushes against the system walls. It manages the pressure level to determine force output. When you need a clamp to hold a part with a specific force, you use a pressure control valve. It maintains the pressure level regardless of changes in flow demand.

• Flow control valve: Regulates how much fluid moves (flow rate), managing speed and volume.

• Pressure control valve: Regulates how hard the fluid pushes (pressure level), managing force.

This distinction is essential for efficiency, safety, and system reliability. Selecting the wrong type of valve can lead to poor performance or dangerous conditions. A system that needs force control but uses a flow valve will not function correctly.

Why Pressure Control Matters in Hydraulic and Pneumatic Systems

Both hydraulic and pneumatic systems need proper pressure control for safe operation. Without it, these systems face serious problems that affect productivity and safety.

In hydraulic systems, this determines the force output of actuators. Too little pressure means the system cannot perform its work. A lift cannot raise its load. A press cannot form a part. Too much pressure risks damaging seals, hoses, and valves. A burst hose can release pressurized oil that creates a fire hazard. Proper system pressure management ensures that equipment operates within its design limits. It also extends the life of components by preventing overstress.

Pneumatic systems face different challenges. Air compressibility reduces precision, leading to less accurate control. You cannot position a pneumatic cylinder as precisely as a hydraulic one. Speed limitations arise from compressed air flow rate constraints. Energy inefficiency is a major concern because compressing air is very energy-intensive. This raises operational costs significantly. Noise from air release requires additional soundproofing measures. Temperature fluctuations and vibrations affect performance. Air leaks reduce system efficiency and are hard to detect. A small leak can waste large amounts of energy over time.

Despite these challenges, pressure control valves remain essential for both system types. They protect equipment, ensure safety, and maintain consistent performance. A well-designed pressure control system helps you avoid costly downtime and repairs. It also improves product quality by keeping process conditions stable.

How a Pressure Control Valve Works

The Principle of Feedback Regulation

A pressure control valve uses a simple mechanical feedback loop to keep pressure at the right level. The valve constantly checks the pressure in the system and adjusts itself without any external power source. This self-contained loop operates automatically, making small corrections many times per second.

The key part of this loop is a flexible diaphragm. This diaphragm senses the downstream pressure through a small control line. When the flow demand changes, the downstream pressure changes too. The diaphragm moves in response to this change. This movement connects directly to the valve plug. The plug opens or closes to adjust the flow. This action counteracts the pressure change and brings the pressure back to the setpoint.

Think of a spring and a diaphragm working against each other. The spring pushes the valve in one direction. The fluid pressure pushes the valve in the opposite direction. When these two forces balance, the valve stays in position. When the system pressure rises, it overcomes the spring force. The valve opens to release excess fluid. This reduces the pressure. When the pressure drops, the spring force wins. The valve closes to build pressure back up. This creates a self-regulating loop that corrects any deviation from the setpoint.

Different valve types use this same principle in slightly different ways. A relief valve opens when system pressure exceeds the spring setting. A pressure reducing valve restricts flow when downstream pressure rises above the setpoint. A sequence valve opens when pressure in the primary circuit reaches a specified value. A counterbalance valve balances load pressure against an adjustable spring. Each type creates a feedback loop that maintains the desired pressure for its specific application.

Direct-Operated vs. Pilot-Operated Mechanisms

You can choose between two main types of pressure control valve mechanisms. Each works well for different situations. The table below shows the key differences.

A direct-operated valve works well for low flow applications. The fluid pressure acts directly on the diaphragm or piston. The spring provides the opposing force. When the pressure rises above the setpoint, the valve opens. This type responds quickly because the diaphragm moves the plug directly. It also works at zero differential pressure, making it good for tank-fed or gravity-fed systems. The design is simple, compact, and inexpensive to maintain.

A pilot operated relief valve uses a different approach. A small pilot valve controls the main valve. The pilot valve has its own spring that sets the trigger pressure. System pressure acts on the main valve through a small orifice. When the pressure reaches the setpoint, the pilot valve opens. This releases fluid from behind the main valve. The pressure drop across the orifice causes the main valve to open. This design gives much better accuracy, requiring only 1-5% offset from the setpoint. It also handles larger flow capacities.

You should choose a direct-operated valve for simple, low-cost applications with low flow. Choose a pilot operated relief valve when you need high accuracy and large flow capacity. Remember that a pilot operated relief valve needs a minimum pressure differential between inlet and outlet to work properly. It also requires cleaner fluid to avoid clogging the small pilot passages.

Common Working Elements: Spring, Diaphragm, and Pilot

Every pressure control valve relies on three main elements to function. These parts work together to create the feedback loop that maintains pressure.

The spring provides the reference force. You adjust the spring to set the desired pressure level. The spring pushes the valve in one direction. In a relief valve, the spring holds the valve closed. In a pressure reducing valve, the spring holds the valve open. The spring force determines the setpoint. A stronger spring means a higher setpoint. A weaker spring means a lower setpoint. The spring works against the fluid pressure to create a balance point.

The diaphragm senses the pressure changes. It converts fluid pressure into mechanical motion. The diaphragm connects to the valve plug or spool. When the pressure changes, the diaphragm moves. This movement opens or closes the valve. The diaphragm is sensitive enough to detect small changes. It responds instantly to keep the system stable. In a direct-operated regulator, the diaphragm senses downstream pressure through a control line. This feedback allows the valve to maintain the desired outlet pressure.

The pilot acts as a signal amplifier in pilot-operated valves. The pilot valve senses the system pressure through a small passage. When the pressure reaches the setpoint, the pilot opens. This triggers the main valve to open or close. The pilot allows the main valve to use the system's own pressure for actuation. This gives much higher force and better accuracy than a direct-operated design.

These three elements work together in a continuous loop. The spring sets the target. The diaphragm senses the actual pressure. The pilot amplifies the signal when needed. The valve adjusts to match the actual pressure to the target. This loop operates many times per second, keeping your system stable and safe.

Types of Pressure Control Valves

You have several options when choosing a pressure control valve for your system. Each type serves a distinct purpose, and understanding the differences helps you select the right one. The table below summarizes the main categories you will encounter.

Pressure Relief Valves

A relief valve keeps your system safe from too much pressure. It stays closed until the pressure at its inlet hits the set level. When that point comes, the valve opens a little to let fluid pass. If pressure keeps rising, the valve opens more to allow more flow. When the inlet pressure drops a few psi below the set level, the valve shuts again.

This cycle relies on two forces that work against each other. The inlet pressure pushes on the sensing part, trying to open the valve. The spring pushes the valve closed. When the pressure force beats the spring force, the valve opens. When pressure falls below the set point, the spring wins and the valve seals shut. This simple loop keeps your system safe by stopping pressure from building too high.

You will find relief valves in boilers, pressure vessels, and hydraulic systems. A pilot operated relief valve gives better accuracy for high-capacity jobs. It uses a small pilot valve to control the main valve, needing only 1-5% offset from the setpoint. Direct-acting relief valves react faster but handle less flow. Both types do the same job: keeping your equipment from failing badly.

Pressure Reducing Valves

A pressure reducing valve does the opposite of a relief valve. It keeps the pressure after the valve at a lower, steady level than the pressure before it. The valve balances the force between an adjustable spring and the downstream pressure. When the downstream pressure goes above the set point, the diaphragm pushes on the spring. This squeeze reduces the valve opening, which brings the downstream pressure back to the set level.

The PRV is designed to limit pressure downstream of its location. Unlike a relief valve that senses upstream pressure, the PRV responds to downstream pressure, ensuring it holds the pressure in the circuit at a safe and steady level throughout operation.

You use pressure reducing valves in water distribution systems, pneumatic circuits, and hydraulic presses. Pilot-operated pressure reducing valves keep downstream pressure steady by using a pilot valve to adjust the water pressure in the diaphragm. This adjustment changes the main valve opening, keeping the downstream pressure constant even when the upstream supply changes. Direct-acting types work well for smaller flows where simplicity matters more than precision.

Sequence Valves and Unloading Valves

Sequence valves let hydraulic parts work in a set order. They open when pressure hits a certain level to send fluid to a second circuit. Picture a clamping cylinder that must hold a part before a drilling cylinder moves forward. The clamp extends, pressure builds, and the sequence valve opens at its set pressure. This lets fluid reach the drill cylinder, starting the second step. You use sequence valves in clamp-and-work circuits, lift-and-tip systems, and other multi-step jobs.

Unloading valves do a different task. They send extra pressure back to the reservoir to keep system pressure within a set limit. You often find them in accumulator circuits and high-low pump systems. When the accumulator reaches full charge, the unloading valve opens. This sends pump flow to the tank at low pressure, saving energy and cutting heat. The valve stays closed until an outside pilot signal tells it to open.

Beyond these main types, you may see counterbalance valves, backpressure regulators, and differential pressure regulators. Counterbalance valves stop loads from running away and keep movement controlled by balancing load pressure against an adjustable spring force. Backpressure regulators keep upstream pressure steady by changing flow based on sensed upstream pressure. Differential pressure regulators keep a constant pressure gap between two separate fluid systems by adjusting valve position. Each of these types of pressure control valves serves a specific niche in industrial applications.

Applications of Pressure Control Valves

Pressure control valves show up in almost every industry that moves fluids or gases. You will see them protecting equipment, keeping processes steady, and making sure operations run safely in many different uses. Learning where these valves work helps you see how flexible and important they really are.

Pressure Control in Hydraulic Systems

Hydraulic systems need pressure control and regulation to stay safe and work well. These valves act as protectors against too much pressure and sudden pressure drops. Without them, machines face damage and workers face serious dangers. A pressure-sensing part, either a spring-loaded piston or a diaphragm, reacts to set pressure limits. This part makes the valve open or close when needed.

Relief valves guard hydraulic circuits from dangerous pressure spikes. When system pressure goes past the spring setting, the valve opens to send extra fluid back to the tank. This stops seal failure, hose bursts, and part damage. Pressure reducing valves keep steady downstream pressure even when upstream pressure changes. This makes sure actuators get steady force for reliable operation.

Sequence valves manage multi-step operations in manufacturing. They make sure one cylinder finishes its stroke before another one starts. Counterbalance valves hold heavy loads in place and control how they lower. Unloading valves send extra pump flow back to the reservoir, saving energy in accumulator circuits. Backpressure regulators keep steady upstream pressure in processing lines. Differential pressure regulators keep a constant pressure gap between two separate fluid systems.

TANGGONG Control Valves for Industrial Pressure Control

TANGGONG control valves give exact pressure control in tough industries. You will find them in petrochemical plants, power generation facilities, and water treatment operations. These valves handle continuous throttling to keep exact process conditions. Their cage-guided trim lowers noise and stops cavitation, even under extreme pressure drops.

The wide size range from DN15 to DN600 fits small pilot lines and huge main pipelines alike. Pressure classes from Class 150 to Class 2500 handle moderate and extreme service conditions. You can pick body materials like WCB, CF8, or CF8M to match your fluid chemistry. These valves support multiple control signals, including 4–20 mA, HART, and Modbus, for easy integration into modern control systems.

Water and Wastewater Pressure Regulation

City water systems depend heavily on pressure reducing valves to protect distribution networks. These valves lower high supply pressure to safe levels for homes and businesses. They stop pipe bursts, reduce water hammer, and cut down on leaks. A pressure reducing valve keeps steady outlet pressure even when demand changes throughout the day.

Wastewater treatment plants use relief valves to protect pumps and piping from overpressure events. These valves open when system pressure climbs too high, sending flow to safe discharge points. This protects expensive equipment from damage and stops dangerous failures. Backpressure regulators keep proper pressure in filtration systems, ensuring steady flow through membranes and filters. Differential pressure regulators help monitor filter clogging by tracking pressure differences across filter beds.

The oil and gas industry uses these valves for wellhead control and pipeline protection. Food and beverage plants rely on them for precise steam control during processing. Steam curing operations for cinder blocks depend on accurate pressure maintenance. Tire curing processes require exact pressure profiles for consistent product quality. Every application demands reliable pressure control to protect equipment, ensure safety, and maintain product quality.

How to Select a Pressure Control Valve

Key Selection Criteria: Pressure, Flow, and Fluid Properties

Choosing the right pressure control valve starts with a clear method. You need to gather process data first, then match that data to valve capabilities. Follow these steps to make a sound choice:

1. Define your process medium and operating conditions. Collect data on the fluid type (gas, liquid, or steam), operating temperature, inlet pressure, outlet pressure, pressure drop, maximum and normal flow rates, specific gravity, and viscosity.

2. Calculate the required flow coefficient (Cv). For liquids, use the formula Cv = Q × √(SG / ΔP). For gases, the calculation includes temperature and outlet pressure corrections. Select a valve size where your calculated Cv falls between 60-80% of the valve's maximum Cv at full opening. This range prevents oversizing, which hurts controllability, and undersizing, which restricts capacity.

3. Choose the valve style and body material. Decide between 2-way valves for throttling or 3-way valves for mixing and dividing. Pick the body material based on corrosion resistance and pressure-temperature ratings per ASME B16.34.

4. Select the flow characteristic. Choose linear for constant pressure drop, equal percentage for varying flows, or quick opening for on-off service.

5. Determine actuator type and action. Specify pneumatic or electric actuators. Define fail-open or fail-closed action based on your safety requirements.

6. Specify accessories. Include positioners, I/P transducers, solenoid valves for emergency shutdown, handwheels for manual override, and pressure gauges.

7. Verify compliance with standards. Ensure your selection meets ISA-75.01.01, IEC 60534-2-1, ANSI/FCI 70-2, and API 598.

The STAMPED method offers another useful framework. It covers Size, Temperature, Application, Media, Pressure, End connections, and Delivery. This checklist helps you avoid missing critical details.

Fluid properties also shape your decision. High viscosity increases frictional forces and pressure drops. You may need larger actuation forces to overcome this resistance. Temperature changes fluid viscosity, which affects pressure drops and flow coefficients. For semi-turbulent or laminar flow, apply viscosity correction factors during sizing. High pressure drops can cause flashing and cavitation. Choose globe valves with low-pressure recovery characteristics to mitigate these effects.

TANGGONG Control Valve Selection Guide

TANGGONG control valves offer a wide range of options for your pressure control needs. The product line covers nominal sizes from DN15 to DN600, fitting small pilot lines and large main pipelines alike. Pressure classes range from Class 150 to Class 2500, handling moderate and extreme service conditions.

You can select body materials including WCB, WC6, CF8, and CF8M to match your fluid chemistry. Trim options include SS304, SS316, SS316L, 17-4PH, Stellite 6, and Tungsten Carbide. These choices let you match the valve to your specific process conditions.

TANGGONG control valves carry ISO 9001:2015, CE, and SGS certifications. They comply with ANSI/FCI 70-2 shutoff standards and IEC 60534 sizing calculations. The valves support multiple control signals, including 4–20 mA, HART, Modbus, and Profibus PA/DP. This compatibility makes integration into modern control systems straightforward.

The company offers free valve sizing consultations based on IEC 60534 standards. Their engineering team helps you calculate the correct Cv and select the right valve for your application. This service ensures you avoid common sizing mistakes that lead to poor performance.

Material and Connection Considerations

Material selection goes beyond the valve body. You must consider trim materials, gasket materials, and seals. Each component must withstand the operating environment.

Brass or cast iron bodies suit low-temperature, low-pressure water or steam service. Steel works well for high-temperature or flammable fluids. Stainless steel handles corrosive products effectively.

Compatibility involves more than the main pipe material. Seats, seals, liners, coatings, and fasteners must also withstand the operating environment. A metal valve body may remain structurally sound while an incompatible seal deteriorates, causing leakage or loss of control.

Your connection type depends on your piping configuration. Threaded connections work for smaller valves. Flanged connections suit larger sizes and higher pressures. Welded connections provide permanent, leak-free joints for critical service. Choose the option that matches your system design and maintenance needs.

Installation and Maintenance

Correct installation and regular upkeep of industrial valves are key for safe and efficient work. Doing both well keeps your equipment running and protects your team.

Proper Installation Techniques

Start by picking the right valve for your job. A ball valve or globe valve works well for pressure control. The wrong choice causes poor performance and early breakdowns. Check that the valve's maximum pressure and temperature ratings are higher than your system's peak conditions. This stops major failures later.

Match the valve material to your pipeline material. Stainless steel, brass, and PVC each fit different fluids and settings. Matching materials prevent uneven wear and contamination. Place the valve where you can easily reach it for operation, checks, and repairs. Think about adding isolation points so you can fix the valve without stopping the whole system.

• Put the pressure-sustaining control valve right after pumps or other pressure-making equipment to control upstream pressure well.

• Follow the maker's instructions for orientation. Make sure the flow direction matches the arrow on the valve body.

• Use proper supports and brackets to cut down on vibrations and mechanical stress.

• Size upstream and downstream piping correctly. Avoid sharp bends and tight spots near the valve.

• Add strainers or filters upstream to stop debris from getting in. Clean and maintain them on a regular schedule.

Choose threaded, flanged, or welded connections based on your pressure, temperature, and maintenance needs. Make sure everything lines up and bolts are tight. Let certified technicians handle accurate alignment, secure connections, and leak testing. This cuts down on errors and accidents.

Routine Maintenance Tips

Set a preventive maintenance schedule and follow it. Regular checks catch small issues before they turn into costly failures. A simple monthly routine keeps most valves running smoothly.

Run closure and leakage tests under full flow conditions. Check for zero leakage when gates are shut. This finds wear or size changes early. Run stroke tests to make sure the valve works under tough conditions. Check auxiliary piping for scaling, rusting, and cracks. Look at bends for pressure damage. Watch for bending or bowing. Check all fittings for loose connections.

Inspect the valve stem and stem nut connector condition. Check actuator shaft alignment and electrical connections. Verify the pressure range and assembly structure. Look for leaks through flange joints or bonnets. Take no shortcuts and follow the maker's advice when fixing valves.

Common Mistakes to Avoid

Many installation problems come from simple oversights. Wrong flange alignment causes leaks and stress. Make sure flanges are parallel and aligned before tightening. Use spacers and tighten bolts in a cross-pattern. Allow 6–10 pipe diameters of straight run upstream. Check full disc rotation without blockage.

Never force a valve open or closed with tools. If it sticks, loosen bolts and check alignment. Check free rotation before pressurizing. Always run pressure tests before putting the valve into service. Start with a low-pressure air test at 2–5 psi. Then hold rated pressure for 10–15 minutes. This confirms the whole assembly works right.

Remember that a relief valve guards your system from dangerous overpressure. Regular checks of relief valves stop unexpected failures. Good upkeep keeps your system pressure steady and your equipment safe. A well-maintained relief valve responds correctly when you need it most. Your attention to these details extends equipment life and prevents costly downtime.

A pressure control valve automatically keeps system pressure at a safe level. It works through a simple feedback loop where a spring and diaphragm balance forces to maintain the setpoint. Common types include the relief valve, pressure reducing valve, and sequence valve. Each type serves a specific function, from protecting against overpressure to controlling the order of operations. A properly sized relief valve prevents overpressure. Relief valves in general protect equipment from damage. Proper selection and regular maintenance prevent costly downtime. Good system pressure control directly improves both safety and efficiency. Apply this knowledge when choosing a valve for your next project. For a reliable, precision-engineered solution, explore TANGGONG control valves. They offer a wide size range, various materials, and free sizing consultations. Contact our team today for expert assistance.

FAQ

What is the difference between a pressure control valve and a flow control valve?

A pressure control valve handles force by keeping system pressure steady. A flow control valve handles speed by controlling how much fluid moves through the system. Each one does a different job.

How does a pilot-operated relief valve work?

A pilot-operated relief valve uses a small pilot valve to control the main valve. When the system pressure hits the setpoint, the pilot opens. This lets fluid out from behind the main valve, which makes it open.

What happens when a pressure reducing valve fails?

The pressure after the valve can go above the setpoint. This might hurt equipment or cause unsafe conditions. Regular maintenance helps catch problems early.

How do I know if my pressure control valve is working correctly?

Check that the downstream pressure stays steady. Look for leaks around the valve body. Listen for odd sounds. Run stroke tests now and then to make sure the valve moves fully.

Can a pressure control valve handle both liquids and gases?

Yes, but you must pick the right valve type for your fluid. Liquids and gases act differently. The valve size and material must match your specific use.

What is the purpose of the spring in a pressure control valve?

The spring gives the reference force that sets the pressure target. It pushes against the fluid pressure. When these forces are equal, the valve stays in place.

How often should I test a relief valve?

Test relief valves at least once a year. High-pressure systems may need more tests. Follow the maker's schedule and your local rules.