A damper orifice is located after the delivery valve. This damper is called a trailing port snubber (Figure 4-79).
The trailing port snubber is used to prevent secondary injections and cavitation errosion of the high pressure system by weakening reflected pressure waves. This port trails the discharge port radially and resonates the fuel back into the delivery valve cavity.
The snubber is drilled directly into the rotor bore and is reduced to .018″ in diameter at the bottom of the hole.
Since it is located radially behind the discharge port, reflected pressure waves will re-enter the rotor after each
injection. The flow rate into the delivery valve bore is then restricted by the .018″ orifice.
Phasing of the rotor snubber port in relation to the other port sequences must be carefully designed. This is
especially true for an eight cylinder distributor pump where rotor angular space is at a premium.
The discharge cycle at each port is about 20 degrees. At the 15 degree point in the injection the snubbing begins
for approximately 22 degrees.
In the oscilloscope traces (Figure 4-80) the reflected waves cause a needle lift in a system with a standard rotor.
With an .018″ snubber port rotor, the pressure waves are reduced and the nozzle valve remains seated between
injection.
This reduces the cavitation erosion potential. In addition, pressure waves reflected from the nozzle are partially,
rather than totally, reflected as they pass through the snubber orifice.
