Safety components are all around us from our cars and phones to our appliances and on our roads. They come in all sizes and shapes but one that we take for granted despite not being hidden is a PRV or pressure relief valve. A pressure relief valve is used in various systems to help keep the pressure inside at a constant level.
The valve opens when pressure rises and it stays so until it drops at a pre-set level. This way damage to equipment and appliances is prevented as well as injuries. Where there's a risk of overpressurisation a pressure relief valve is used and at home, it's most commonly found in a water heater.
What to Look for in a Pressure Relief Valve
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| source: maroochydorehandyman.com.au |
Material
Water pressure relief valves are made of various materials but bronze and stainless steel seem to be the most common. There are also relief valves made of brass but they are not as strong. However, a cast gunmetal hot water tank pressure relief valve is a great alternative to both bronze and stainless steel thanks to its impact resistance and high ductility together with its remarkable compressive and high tensile strength.
Set Pressure
Another important aspect of a water pressure relief valve is its set pressure limit. This is the pressure at which the water pressure valve opens up to help keep the system in question operating at its ideal pressure. For instance, if you have a system with a pressure of 2000 PSI the set pressure limit should be at 2300 PSI. A difference of 300 PSI is a safe difference. Of course, it's not the same for smaller systems, as the pressure of said systems is much lower.
Capacity
The valve capacity refers to the amount of water that's going to flow through. The larger the valve capacity the more water can flow and thus the quicker the valve is able to relieve the system from that extra pressure. But this also affects compatibility with inlet and outlet ends as they need to match in order for the pressure relief valve to be installed.
Back Pressure
Talking about the valve's outlet, if it has too much back pressure it can end up damaging the valve. This can also reduce the set pressure of the valve and make it open up uncontrollably. Make sure that the back pressure is always about 10% below the set pressure limit.
Temperature
What the material of the valve affects is the temperatures the component can take on without issue. Both the medium and pressure levels are controlled by temperature and having the valve keep a certain temperature level present is key.
Positive Reseating
A water pressure relief valve with positive reseating is one that reseals itself when it blows under pressure. When the pressure drops to the normal level of the system, the valve reseats with the help of either a soft seating design or a metal-to-metal interface. The former is better since it's not prone to leaking like the latter.
Types of Pressure Relief Valves
Conventional
With a conventional relief valve, you get the most basic solution that has an instant pop-up action mechanism that works best only in systems with low back pressure. That's because a conventional relief valve has its working pressure and relieving capacity heavily influenced by high back pressure.
Balanced
A balanced hot water tank pressure relief valve is a component that operates on a loaded spring paired with a bellow to help maintain optimal pressure levels. Unlike a conventional relief valve, a balanced one is best suited in high back pressure applications.
Full & Low-Lift
Both full and low-lift safety relief valves operate thanks to discs that move inside according to how much pressure needs to be released. A full-lift relief valve will have its disc moved from its original placement about 1/4 of the bore's diameter. A low-lift valve has the disc lift 1/24 of the bore diameter. The former are best for steam boilers while the latter are used in pressure vessels and piping systems.
Full-Bore
Full-bore relief valves also have discs but the amount of pressure they release or the flow of the water is not determined by it. Instead, here the nozzle is what affects this as the valve seat passage is equal to the nozzle of the valve seat area once the valve opens. This means the distance of the valve's rising to falling action is what affects the amount of discharge flow.
Conclusion
A water pressure relief valve is one extremely important yet often overlooked safety component that can save both the system it's on and your home or workplace from lots of damage and unwanted spendings. The simplicity is what makes it so good at controlling pressure which is also the reason why you shouldn't skimp on one.
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