Technical Notes

Diagnosing Injector Problems

Miniature injectors can be a very reliable way of feeding water to boilers.  However, care must be taken in the installation and operation.  The following notes have been provided by one of our very experienced injector manufacturers, JC, and will be helpful to all those struggling to make injectors work.  Injectors are precision engineered devices and inferior quality injectors cannot be expected to perform as well as the higher quality ones.  However, in most cases as the notes explain problems of injector behavior are more likely to be due to installation or operational considerations, such as undersized clacks, air leaks or simply muck in the water.


Don’t Automatically Blame the Injector

The miniature injector supplied by reputable dealers these days can be relied upon to do the job it is intended to do, BUT there are some simple do and don’ts that must not be ignored.

  1. The injector must be supplied with all the steam it needs without restriction.
  2. The injector must be supplied with all the water it needs, filtered, without restriction and absolutely air free.
  3. The injector must be cleared of all the water it is delivering without restriction.

There are no compromises to be made with any of the above and still guarantee that the injector will work properly.

There are no particular demands on pipes provided the internal cross sectional areas are not reduced in any way by flattened bends or over generous silver soldering resulting in partial blocking of pipes. Off importance is the overall area of the water filter. Even 90 degree bends are tolerated. If the reader thinks differently he should consider why 90 degree steam valves, 90 degree check valves and vertical injectors do not stop the system in its tracks.

Why then is so much trouble experienced by so many people?

With the correspondence and phone calls I receive from time to time, and one to one conversations on numerous steaming bays, it becomes clear that a large number of modellers are looking at the injector in isolation, whereas in truth it is part of a complete system ,from the steam space in the boiler from where it receives its steam supply, to the steam space in the same, or in rare cases different boiler. Included in the system, is the steam manifold, every pipe, steam valve, water filter, water valve, and boiler check valve. All of these parts must carry without restriction all the flows to and from injector. YOU IGNORE THIS AT YOUR PERIL.

The water supply to the injector must also be air free. This should be interpreted as ‘there should be no chance whatever of air getting into the system from water valve glands loose fitting rubber pipes or for any other reason’. Nothing less will do. Try drinking a glass of lemonade through a straw with a small hole in it. I’m afraid you will not make much progress, and neither will the injector, which is also trying to suck the water. YOU IGNORE THIS AT YOUR PERIL.

Check also for rubber feed tubes being sucked flat. There must be in place a water filter of sufficient an area to allow full flow to take place and which is capable of filtering to the smallest dimension of the combining and delivery cone entrances in order to stop a particle of any shape getting into the system Remember those holes in that injector are tiny. YOU OMIT GOOD FILTERING AT YOUR PERIL.

There is a problem that can occur from time to time in hard water areas, and it would seem that all water companies are adding salts to the supplies, even in areas where the water was once considered as soft as the mountain dew. The symptoms are thus. On first fitting the injector it works for a period quite satisfactorily. After a period of non-running, usually over the winter, the injector, when first tried, begins to spit at the overflow and generally ‘plays up’. It may or may not deliver water at all. After a time the problem may possibly clear and the injector will work fine. My own theory is that during the layoff the water remaining in the pipes has dried out and left a deposit of hard salts which are insoluble; these of course have already passed the filter, so should they break free you will be in trouble. It is very interesting to note the number of times over the years that I have encountered this problem.

My own method of attacking this problem is as follows. At the end of the season, or before a period of non running, and while still in steam, I disconnect the water feed and replace with a temporary rubber tube feed into a jar of citric acid solution. The steam is turned on, but only enough to pull the water through the injector and out of the overflow, but not into the boiler. The mixture is caught at the overflow and re-used until the fluid is quite hot.

This will make sure the injectors’ sensitive bits will get their fair share of acid. This method is easier if the injector is of the lifting type.

The water delivery to the boiler should be treated with the same regard to pipes and passages as previously stated and added to this There must be sufficient annular clearance around the ball for full flow to take place, and the ball must be physically restricted from trying to enter the outlet port of the valve. If the ball can get into the boiler it will! I must point out at this time that off all the injector problems I have solved at least 90 percent have been the check valve. YOU IGNORE THIS AT YOUR PERIL.

A recent discovery is that model engineers are apparently being recommended to put a cage with a cutout around the ball in check valves, presumably to contain and guide the ball. The problem engine I was examining when this came to light. Stopped working above 90 lbs but I new full well it would work at its designed pressure of 125lbs. This cage/ball arrangement stopped the injector working properly by greatly restricting the flow of water through the check valve. A check valve used with an injector is a slow operating device and designed properly will require no assistance from such a cage and, as in this case, can even find it detrimental to its working.

I would think twice about being tempted to use rubber balls in boiler check valves (or anywhere else). I well remember digging the remains of three rubber balls from the inlet pipe to a Dutch check valve that had an ‘injector that did not work’. After fitting a stainless steel one the injector worked fine. The amazing thing was that the user, at no time questioned where they were disappearing to but simply put in a new rubber ball!!!!!

Think carefully about the pressure the injector should be working at and the accuracy of your pressure gauge. I had a problem once with an injector that wouldn’t work and after testing the engine pressure gauge found the boiler was working in fact at165lbs instead of 100lbs as shown by the gauge. After the appropriate treatment to the safety valves the injector worked fine and the owner was able to exercise a much better control over the regulator. It sure is a funny old world.

If you have everything needed in place you should have an injector that will work bone dry at the overflow at designed working pressure, steam or water on first, will exhibit a decent dry working range, will be self starting with the steam and water valves full open, until the falling boiler steam pressure requires trimming of the water valve to compensate, It should even be possible to start and run the injector at a ridiculously low pressures by reducing the water input. Think in terms of chasing the dribble with the water valve.

The injector, filter, and water feed pipes will require cleaning from time to time especially in hard water areas and this is done in citric acid at between 25gms (1oz) and 50gms (2ozs) per litre (2pints) water. Do not simply drop in and leave, but remove and clear liquid from inside the injector and replace in the acid from time to time in order to replenish the exhausted acid from the interior. Citric acid is kinder to the metal than some of the others. I have examined injectors after being naively put into some quite ferocious (some fizzy drinks fall into this category) brews and the result is not a pretty sight.

If success still eludes you, now is the time to contact your supplier.