While some engineers swear by such a three-tiered safety approach for high pressure pump system defense, others feel this much redundancy is unnecessary and a safety valve and unloader in combination is sufficient. Nevertheless, it is important to remember that thwarting any valve or other safety device is courting disaster and should never be done.
Aside from the unloader, a second line of high pressure pump system 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.
Consequently, some engineers suggest a third safety measure – a rupture disk. This disk is engineered to burst at a certain pressure, usually a bit above the machines rated operating pressure to allow for normal pressure spikes. In other words, the disk, which can be screwed into a port on the high pressure side, is a non-adjustable artificial weak point in the system.
Disks which are heat sensitive – the solder melts at high temperatures, are also available as safety devices for hot water machines. This system of preventing coil overheating was long used by a pioneer steam cleaner manufacturer.