Injector or pump?

[steelaxleboxParticipant @steelaxlebox]

Is there someone scientifically minded who can explain the advantage of an axlepump over injectors (or vice – versa) for locomotive boiler water feed? I'm thinking in terms of whether a pump or injector requires more energy from the boiler/cylinders than the other.

Other matters like ease of use I'm ignoring; it can be very fiddlesome getting an unhappy injector to play whilst on the move but obviously an injector will feed when you are standing still.

I'm asking the question because advancing years are making my leaning and stretching feel uncomfortable. A pump equipped 3.1/2" King (H P Jackson) I built decades ago seemed so simple to drive but I accept that time has rose-tinted my specs! 5" gauge tender locos and age are returning me to the debate.

[steelaxleboxParticipant @steelaxlebox]

[Neil WyattModerator @neilwyatt]

Injectors are much more efficient. They are thermodynamically efficient (about 97%) with virtually all the energy loss being limited to heat loss from the system

While axle pumps have to deal with moving parts and therefore friction etc. they can still be quite efficient, but as they are driven via the motion which is, say, ~2% efficient they will use much of the available energy in the boiler.

Neil

[Paul LousickParticipant @paullousick59116]

There should be 2 ways of adding water to the boiler. Either a pump and and injector or 2 injectors, in case one of them fails. I drive a full size traction engine and find it far easier to use a pump while moving. There are too many things to do if you are driving down the road (especially with only 1 person). eg. Watch the road and steer the engine, monitor the water level, feed the fire and turning one valve to feed water is simple. If using the injector you have to turn on the water and then the steam. Sometimes the injector fails to pick-up the water. Pressure differences affect the injector and they like a steady flow of steam or will fail to work. Sometimes the injector will not work if under load, chuffing up a hill and you have to slow down or stop the engine. Injectors are great when stationary because you do not have to put the gears into neutral and turn over the engine to run the pump. Both have their good and bad points and having one of each is an advantage.

Paul.

[DMBParticipant @dmb]

If practicable, better design of pump drive is by crosshead thus eliminating friction at the eccentric and pin joint on pump ram together with excessive ram and gland wear caused by eccentric rod waggle.Easily disguised on models of GWR locos as the vacuum pump but if on other types could be part hidden by running board/valance.
Furthermore, only a longish gland nut need be in rubbing/friction contact with the pump ram since the cylinder bore can be made larger than the ram. The ram would then be a displacer still pumping effectively without much friction and with another benefit of being air-lock free. Bill Stroudley’s design in full size.

[DMBParticipant @dmb]

The late Martyn McBrien was planning to fit twin Stroudley pumps to his 6 wheeler Sweet Pea. That scheme means an equal pump load on each power cylinder at 90* thus evening out pumping effort as opposed to all the load being in applied in a part revolution with the use of eccentric drive. Martyns loco now a Worthing club loco and can be seen passenger hauling.

[wendy jacksonParticipant @wendyjackson]

I have taken out the injector from my Pansy as it never worked and was just a pain. the water valve setting was so low in the cab space that I could not turn it on with ease. The pansy is fitted with the hand pump and crosshead pump. I have also fitted a 12v electric pump in the riding truck as back up. hate injectors and have seen so many people not going on the track due to injectors playing up. michael

[Harry WilkesParticipant @harrywilkes58467]

I agree with Paul I have a 3" Burrell and I don't use the injector when on the move, small injectors can be a 'pain in the butt' mine is so I only use it when ticking over !

Posted by Paul Lousick on 15/02/2015 00:05:35:

There should be 2 ways of adding water to the boiler. Either a pump and and injector or 2 injectors, in case one of them fails. I drive a full size traction engine and find it far easier to use a pump while moving. There are too many things to do if you are driving down the road (especially with only 1 person). eg. Watch the road and steer the engine, monitor the water level, feed the fire and turning one valve to feed water is simple. If using the injector you have to turn on the water and then the steam. Sometimes the injector fails to pick-up the water. Pressure differences affect the injector and they like a steady flow of steam or will fail to work. Sometimes the injector will not work if under load, chuffing up a hill and you have to slow down or stop the engine. Injectors are great when stationary because you do not have to put the gears into neutral and turn over the engine to run the pump. Both have their good and bad points and having one of each is an advantage.

Paul.

[Halton TankParticipant @haltontank]

Being a belt & braces guy, I have both, axle/crosshead pump and two injectors on my locos. To make it easier to operate injectors when on the move I have extensions fitted to the overflow of the injectors so I do not have lean over to see if the injector is operating (OK not prototypical, but better than me falling off because I lent too far). Also as my engines are tank engines I have a separate water supply on my driving skate to feed the injectors. The tanks on the loco feed the axle/crosshead and the hand pump.

Injectors are not maintenance free, especially if you using hard water, so after each run I take my injectors and give a clean in citric acid using an ultrasound bath. Since I have been using this regime I had little trouble with injectors.

I also blow my boiler down after each run, this stops muck accumulating in the boiler and clagging up clacks that are at the bottom of the firebox.

Regards

Luigi

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