Recently we had a Harben ‘P’ Pump returned for some repair work to a cracked delivery nut.  Without having to look any further the service technician knew straight away what had caused this issue.  Our customer had replaced the pressure disc, otherwise know as the safety rupture disc, with a foreign object.  Unfortunately, all too often we see pressure discs replaced with coins, pieces of plastic or the disc holder removed and capped off completely!  Altering the pressure disc system creates a dangerous and potentially costly situation.

Why do I need that disc?

The purpose of the pressure disc is quite simple; the disc prevents the pump from over pressurizing and creating a situation in which the pump could literally destroy itself.  On some pumps the pressure disc is the only thing that stands between the pump running a long continuous life and the pump pressurizing out of control.  On a Harben ‘P’ Pump, the inlet and delivery nuts are made of brass, a softer metal than the stainless steel barrels.  The brass will ‘give’ should the pressure disc not do its job and burst when over pressurized.  However, not all pumps are built as well as a Harben Pump and may not offer this failsafe.

Why do my discs keep bursting?

While the pressure disc is intended to burst, it should be understood that a pressure disc that continues to burst over a short period of time is an indication of a problem.  The disc is designed to fail at a set point and this is usually when the pressure reaches about 10-15% over the disc rating, e.g. a 4000 psi disc may bust at 4400 psi.  There are many reasons for a disc to burst, some common examples are: the nozzle tip could be clogged, using a mini jet hose that is too small for the application or using a nozzle that was not configured with the right flow and pressure for the unit being used.  It is also worth noting that heated water can soften a pressure disc, causing it to prematurely burst.  The heated water can be generated from your hot water tap, but also the sun warming the water  in you tank on a hot day.  However, a jetter operating with the right tools and accessories will not continually burst discs.

Are the different colors relevant?

Each pressure disc is color coded to indicate the pressure that it is rated for.  Never use a pressure disc that is rated for a lower pressure than your jetter is capable of producing.

What about an unloader valve?

Although an unloader valve may be used we recommend the pressure disc system as unloader valve can corrode over time causing it not to function properly.  This can then allow the ‘unloading’ of the built up pressure which in turn means that the pump can over pressurize.   A pressure disc system will never allow this situation to occur.

The value of a pressure disc

What is the value of a pressure disc?  The cost of a pressure disc is just a few $’s.  The cost of an unloader valve can be upwards of $500.00.  However, the cost of repairing or even replacing your pump because of failing to use a proper pressure disc system can be much higher.  Yes, replacing a burst disc can be a nuisance, but it is a nuisance that is very ‘wallet’ friendly and will help keep your investment up and running.

If you have any questions about your pressure disc system or would like to learn more about Harben products, please
contact us.