There are many possible fundamental causes of valve failure and it is the purpose of this presentation to examine these and trace some of the more common failures which can be attributed to operating conditions beyond the control of Laxmi Rock Drills.

Head Facture Mechanical Failure Valve Seat Failure

1. A piece broken away from the valve head roughly in the shape of the chord of a circle due to very high cylinder pressure and valve temperatures; incorrect valve material; etc.

2. Concavity of the back of the valve head due to very high cylinder pressures and valve temperatures

3. A piece broken away from the valve head roughly segmental in shape, or a radial rim crack propagating inwards due to excessive valve temperature together with unequal cooling .

1. Valve head to stem breakage in the region of the junction of the under head radius with the stem due to excessive cyclic stem stresses brought about by valve bounce due to over speed or weak valve springs, seating velocity too high due to excessive tappet clearance or loss of valve retainer.

2. Valve stem breakage through cotter groove due over speeding or valve bounce.
w Excessive valve stem and guide wear due to too much valve stem to guide clearance; poor stem lubrication; poor stem to guide alignment.

3. Valve stem sticking or seizing due to lack of lubrication; not enough stem to guide clearance; bent valve stem; carbon build up at the bottom of the valve stem, incompatible valve to guide material.

4. Exhaust valve seat wear due to incorrect fuel; valve seat misalignment; weak valve springs worn guides.

1. Valve burnt out locally in a deep channel or gutter due to poor seating due to cold sticking; lack of tappet clearance; excessive carbon buildup; misalignment; worn valve guides; pre-ignition; etc.

2. Wide areas of valve face burnt and blowing but no guttering due to poor valve seating in affected areas; worn guides; excess material removed from and during previous re-facing operations.

3. Badly pitted valve and valve seat faces, discovered on early overhaul due to power loss or a burn out due to excessive oil consumption, incorrect mixture setting producing a high level of solid particles or long periods of low power cold running.

4. Exhaust valve undsser head or back of head surface corrosion due to Excessive overload and overheating or incorrect fuel.

5. A hole burnt through the back of head in the under head radius, just behind the seating face due to this is another form of the radial rim crack (Head Fractures) or thermal fatigue, burning through beyond the hard seat face.