We show you how to simply set a hydraulic pressure relief valve to the correct pressure in your hydraulic system.
Relief valves are used everywhere. They are designed to limit the pressure in a chamber or system. That is a big deal if safety is involved. Here are a few examples. Here is a low pressure relief valve set at about 8 bar to protect an air receiver. Here is a neat Nupro pipe check relief valve adjustable up to 40 bar. Here is a cartridge relief valve that screws into a manifold for oil hydraulics. There is even a miniature relief valve built into the lid of a pressure cooker.
Some relief valves are factory set and can’t be adjusted. Some are safety accessories and you mustn’t adjust them. Others have to be set to suit your operating pressure. All will only work best over a certain range with a particular spring and orifice. Look at the data sheet to check your required setting is in the range or you won’t get very good performance.
I’m looking at this little cartridge relief valve that we fit to our Micropac pumps and I am going to set it to meet my pressure requirement.
This is a small direct acting relief valve that we use screwed into the side of our Micropac pumps. Let’s look at the basics of this. A plunger with a cone is pressed into an orifice using a spring. This seals and won’t let flow past. Let’s increase the system pressure and at some point the force generated over the area of the orifice simply lifts plunger out of the orifice against the spring load. The pressure is vented or relieved back to tank or to atmosphere as the relief valve opens. We call this the cracking pressure. The plunger moves back again under spring load as the pressure is now lower and reseats again.
If the relief valve is adjustable, it is probably using a screw to adjust it. On our Micropac valve, we need to unscrew the dust cap to expose a hexagon socket on the end of the adjusting screw. Let’s cycle the hand pump to see what it is set at now. It looks like 30 bar. I want to set it at 60 bar, so carefully turn the adjusting screw clockwise to load up the spring. You would turn anticlockwise to reduce the pressure. I am only turning a few degrees to get a feel for how sensitive it is. You don’t want to ram the plunger into the seat and damage it. Right, we are up to 60 bar, so let’s take it that final bit. We will release the pressure and take it up from zero. Yes, that is good, Test once again. Now refit the dust cap.
So that is our relief valve adjusted on this Micropac pump. This is only a simple direct acting type. Remember, relief valves are often safety accessories under the Pressure equipment directive so they will need to be an approved type in that case. Go very easy with adjusting a relief valve. Lots of small adjustments are better than damaging the valve. And test it before you finish.
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