Oil pressure relief valve HMB, 4 Bar

New HMB-Design !

The pressure relief valve has an important function in the Moto-Guzzi engine. It must keep oil pressure steady, under all conditions. When rpm is low, it must be closed completely to avoid pressure losses. When oil pressure rises above 4 Bar, the valve must open to avoid higher pressures as these may damage the engine.
The original valves work, but they wear. Pistons get leaky, springs wear in way that makes them break, the latter causing pressure loss and severe engine damage. As in our manufactory engines, we used to order brand new valves, set them up to correct pressure etc. But now, quality issues force us to react. Some of those brand new valves turned out to be be rusty inside, which made them jam in open position. Again, this would have caused severe engine damage because of collapsing oil pressure.

So we designed a new valve with many advantages. Besides local precise CNC manufacturing, we use antimagnetic steel, for the case that magnetic debris (sometimes caused by deteriorating magnetic oil plugs) is in engine oil. The oil that is blown out of the valve, is blown out under the oil level in the sump, thus avoiding oil mixing with air and causimg foam.

As CNC machining is extremely precise, the fit between the valve piston and its seat does not allow leakage below the nominal blow-off pressure. The internal spring is almost twice in diameter of the original, making a stable setting of the piston possible, as well as a far longer lifespan.

All these features contribute to a steady oil pressure !