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The world is home to millions of homes equipped with water heating systems, such as boilers or water heaters. When these devices overheat, internal pressure can rise dangerously, potentially leading to catastrophic failure. While rare, a ruptured tank can cause significant damage—sometimes even launching the unit through the floor and roof of a house. How can we rest easy knowing such a risk exists in our basements?
The answer lies in a small but vital component: the Temperature/Pressure Relief Valve (TPRV). Typically located on the side or top of the tank, this spring-loaded valve opens when pressure or temperature becomes unsafe, releasing excess water to reduce internal stress and prevent explosions. (See Figure 1)
This valve usually remains dormant, only activating in emergencies. Like a car’s airbag or a building’s sprinkler system, it’s designed to be ready for action without ever needing to be used. However, its presence is crucial for safety.
In industrial settings, pumps are used to move liquids through complex systems. As they operate, pressure builds due to factors like head pressure, friction, or resistance from filters and meters. While pumps are designed to handle normal conditions, real-world variables can cause unexpected pressure spikes.
Kinetic pumps, such as centrifugal or turbine types, adjust their flow rate based on pressure. If downstream blockage occurs, they may slow down or stop entirely, reducing the need for overpressure protection. But rotary positive displacement pumps, like gear or lobe pumps, maintain a constant flow regardless of pressure. This means that if a blockage occurs, pressure can build rapidly, risking damage to the pump or system. For these, overpressure protection is essential, and relief valves are commonly used.
Relief valves typically feature a spring-loaded poppet mechanism. Under normal conditions, the spring keeps the valve closed. When pressure exceeds the set point, the valve opens, allowing some fluid to bypass back into the system. The adjusting screw allows users to fine-tune the pressure setting.
Important Note: This information applies specifically to Viking Pumps. Other manufacturers may use different designs, including fixed-pressure valves or ones that require the pump to be shut off to close after activation. Always consult the manufacturer before installation.
There are three main types of relief valves used with Viking Pumps. Internal relief valves are built directly into the pump, offering a compact solution. They redirect flow internally from the outlet back to the inlet, which can make it hard to detect when they’re active. They also risk overheating if operated at full bypass for long periods.
Return-to-tank relief valves direct excess flow back to the supply tank via piping. This helps dissipate heat and makes it easier to monitor when the valve is engaged. These are often standard on certain models, such as the Viking 4924A Series ammonia pumps.
Inline relief valves are installed in the discharge line and are ideal for systems where frequent bypassing is expected. They should never be placed between the pump and the valve, as this could lead to overpressure. A second relief valve may be necessary in such cases.
While it sounds counterintuitive, the perfect relief valve is one that never needs to open. It's not a flow control device or a pressure regulator—it's there to protect the system in emergencies. Just like the TPR valve on a water heater, multiple layers of protection are recommended, including rupture discs, pressure transmitters, and motor protection.
Many Viking pumps have operated for decades without ever needing their relief valve. Yet, its inclusion is essential for preventing dangerous failures. Often overlooked, the pressure relief valve is the silent guardian of your pump system—always watching, always ready.