The Second Line of Defense
Aside from the unloader, a second line of defense is the safety or pop-off valve, which is set to release water to the atmosphere when a set pressure is exceeded. However, this valve can be adjusted as well, usually with a screw driver.
The valves are built for a certain range of pressures, say from 2,000 to 4,000 psi and a safety valve can easily be adjusted, or improperly adjusted, to the point where it no longer functions as a safety device.
Instead of the safety valve functioning as .an artificial weak point in the machine, over pressurization may cause a rupture at a real weak point, perhaps with disastrous results.
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