On my turbo car its highly recommended to have blow off valve which when you shift and the throttle blades close a surge of air crashes back against the compressor which is hard of the compressor and really slows the wheel down. I know we dont have a throttle, but wondered if anything familiar occurs with a diesel. After all there a number of diesel people breaking turbos, and never heard of a Holset on a turbo car breaking.....

I never heard of a blow-off valve or anything like it on a turbo diesel. My truck (1992 Dodge CTD) or my car (1984 Mercedes-Benz I-5TD) are both turboed diesels and they do not have anything like that on them. This might just be me, but it seems like the only people that break turbos are the ones who have done performace upgrades, and it just gets to be too much for the turbo... I am not sure though.

Number one cause of turbo failures is an oiling problem. Besides that, just plain wear and tear will eventually cause a turbo to fail. When a blow off valve is not used on a car with a throttle body, the shock of the throttle body rapidly closing will put a strain on the compressor wheel and cause accelerated wear on the bearings. But like you said yourself, diesels don't have a throttle body so that issue isn't present.

Yeah, the throttle body closing causes major compressor surge even at low boost levels. Lots of hopped up ricers that run HX-40's are very familiar with the weak shafts breaking becuz of the surging. Hence, blow off valves are a must and sometimes they dont clear out the boost quick enough. I wish I could rig one up to my diesel somehow. It would be much easier on the turbo and keep her spinnin. This would take care of all of the barking you get from stock turbos that are way off the efficiency map (aka lotsaboost!). Even though a throttle isn't present, the sudden drop in RPM's is enough to make some of the air kick back out. Holset's simple solution is the slotted compressor housings.

Yeah, the throttle body closing causes major compressor surge even at low boost levels. Lots of hopped up ricers that run HX-40's are very familiar with the weak shafts breaking becuz of the surging. Hence, blow off valves are a must and sometimes they dont clear out the boost quick enough.... Even though a throttle isn't present, the sudden drop in RPM's is enough to make some of the air kick back out. Holset's simple solution is the slotted compressor housings.

+ a lot more RPM / air volume in the gassers. If you are driving as a diesel truck (i.e. matching RPM - shifting w/o clutch (to preserve torque shock on components) Turbo will be happier, If you are drag racing, might want to change your strategy. (or vehicle)

There are BOV's for diesels, but they are not a real important saftey feature on a diesel. No throttle blades. :)