Injectors are excellent when they work But are trouble when they don't.

The boiler on my Ruston Proctor traction engine is slightly smaller than yours and holds about 45 litres. A good, free flow of water is important and lots of sharp bends should be avoided, especially from the tank to the injector.

I use No 6 horizontal injectors, rated at 4 pints/minute which are a good size for my engine. Filling the boiler with too big a volume of cold water can cause thermal shock or a quick drop in pressure.

I originally ordered 2 injectors from the company that supplied the castings but had problems with them. Replaced them with another brand and have had no problems.

The water supply to the injector and the outlet to the clack valve uses 5/16" OD tube (not pipe that is sized by its nominal bore). Check that the injector connections are correct as I had to exchange those that I had ordered because the supplier did not know the different standard between pipes and tubes.

Possible problems:

The flow restrictions caused by acute bends – you have mentioned that one.

From that though, are the clacks appropriate for the injectors? If too small they might create enough back-pressure to upset the injector.

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Air-leaks on the suction side – the very devil to locate because by their nature they don't show unless in, or upstream of, the water valve, and sufficient for water to ooze out. One clue that this is happening, is the injector feeding the boiler, but chirruping like an excited guinea-pig in the process, and occasionally spitting hot water from the overflow. They should run quietly, with a fairly steady sound of rushing water.

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Is the injector too large for the steam supply available? That might be what the boiler inspector had in mind. The pipework may be right but is the steam-valve and the passage to it through the manifold, of comparable size?

Injectors need be matched not only to steam and water supply but also to working pressure-range. They can be fussy about these, and though this is not intuitive it seems they can also have too much water! More accurately, they want plenty of water at the inlet, but then the water flows through a very tiny annulus between the steam and combining-cones, and the geometry there is not normally adjustable but is critical to the device's behaviour for a given steam flow and pressure. (My own club's 'Wren' has an injector that needs the water choking back almost to the point of closed, to make it start – that should not be necessary.)

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To answer Paul's point about water temperature, injectors want cold water into them, but they do not feed cold water to the boiler. They are actually moderate feed-water heaters! They rely on the heat energy in the steam for their operation, and although much of that is converted to the kinetic energy in the moving water, the rest stays as heat absorbed by the water. The water is not so hot that it maintains the water and steam conditions, but is still hot enough not to worry the boiler's structure unduly, especially if the feed-clack is away from the firebox – as is normal on locomotives.

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It's worth buying a copy of Doug Hewson's book on injectors. Though mainly describing how to make ones that work (many of us do seem to think injectors are among the Black Arts) he covers areas like servicing and fault-finding. He also makes, and explains, the interesting point that a miniature locomotive should not need an axle-driven pump. Model traction-engines do, because their prototypes do; but almost all full-size locomotives relied on injectors. Though making a working, BR Standard pattern, exhaust-steam injector for a 5"g locomotive, might be off-limits!