turbos and switching

[ShaunCN]

how well did/do engines fair while switching when eqiped with a turbo, say a GP38 is it better than a GP40 with it's turbo or SD45's? just curious as i heard that slow swithing wrecked havoc on the turbos over a long period of time.

[Tulyar15]

I believe the UP turbos had a small diesel engine for switching moves.

The version of Jetrain that Bombardies were proposing in Britain would have had a small diesel engine for such moves.

[kenneo]

EMD's turbo-equipped locomotives have a clutch that engages the turbo after the diesel engine reaches a specific power level. Switching causes this clutch to continuously engage and then disengage thus causing excelerated wear on the clutch. While the turbo is disengaged, the diesel runs on what is called "normal asperation" which, in reality, is a Roots blower providing about 4 lbs positive pressure to the cylinders.

As a practical matter, EMD locomotives greater than 2300 HP are no better at switching than the lower HP units. The reason is that the engines can not develope any greater HP than the lower HP units at the lower throttle positions without the delay you mentioned. There are several reasons for this - mostly electrical. There are solutions for this problem, but the railroads don't normally use them since they don't normally use these kinds of locomotives for switching.

The other builders mounted their turbos with direct drive, which causes the smoke cloud when the units are accelerated (called turbo lag).

[M636C]

Eric's explanation while basically correct, has a couple of problems. The EMD turbo replaces the roots blower on turbo equipped engines, The turbine is rigidly attached to a centrifugal compressor which does the compressing of the air. Both of these are connected through an overunning clutch to a gear train from the crankshaft. Up to Notch 7, the compressor is driven by the engine but beyond that the exhaust pressure is enough for the turbine to take over and the clutch releases. As the engine slows down when notched back, the clutch re-engages (the final drive gear is fitted with springs for absorbing the shock of this happening).

If the switching can be carried out without going beyond notch 6, there should be no problem, but if this isn't enough, the clutch will be working overtime releasing and grabbing again.

For this reason, SD38s are popular as switchers, and older SD40-2s can be converted to blower engines for this purpose.

Alco and GE engines are not fitted with any drive to the turbo and will be slower to throttle up, and this is one reason GEs are unpopular for this duty, and are said to be slow to load up.

M636C

[jchnhtfd]

M636C and Eric just about cover it -- one might add that one reason that Alcos and GEs tend to smoke while notching up is that turbo lag.

Non-turbo engines were much better for switching; as noted, the horsepower isn't needed (just the tractive effort) and there's no point in paying for a turbo and the maintenance if you don't need it!