The Quest of the Fool-proof.
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An Interesting Story of the Evolution of a Satisfactory Oil Pump and the Minute Investigation which its Production Entailed.
By Henry McLaren.
Since the general introduction of high pressures and of superheated steam, combined with high piston speeds on steam wagons, the proper lubrication of the cylinders has become of great importance, especially if the engines are to go into the hands of ignorant men.
Practically the whole output of toy firm is for export trade, and it is an amazing fact that our customers in many part of the world are willing to pay high prices for their engines, and yet, when they get them, are content. to put them in the hands of drivers who have not the slightest glimmer of intelligence.
The Necessity for rool-proaness.
For the past 36 years I have been trying to design engines that will give useful results in the hands of such men. Long ago I came to the conclusion that to attain any measure of success, every detail must be made absolutely fool-proof." But one must first know the measure of the fool, and this cannot be obtained in the drawing office, or in the testing shed at home ; one must study him in his lair. For many years I have done so, and have, as a matter of fact, travelled the world over in quest of him. Never yet have I failed to come home with my notebook fu1.1 of him and his ways.
Lately his troubles with the cylinder oil-pump have had a prominent place in my notes. Most oilpumps will give more or less good results in the testing shed, or at home in the hands of .competent drivers, but when they get abroad, especially in hot countries, and in the hands of such men as I have mentioned, I have so far not found one that. is absolutely " fool-proof."
Check Valves full of Fluff.
For two months I had an engine under close observation ; it was worked by native labour in a very hot climate. I found that the check valves, on the delivery side of the oil-pump, became choked and so stopped the oil supply ; this happened on an average once a fortnight. When cleaning out, we always found that the obstruction' was a plug, composed of fluff from cotton waste, and of a fine vege
table substance, something like oat chaff, only lighter. The engine was working in a constant cloud of this stuff, so we understood where that came from ; and on further investigation we found that the cylinder oil kettle, filled with oil but without a lid, was kept buried under a heap of cotton waste. The large oil bottles were also corked with waste instead of corks.
Thus the obstructive material was accounted for, but why should it get into the check valves, and why did the pump not force it through into the steam chest? The first query was easily answered, for we found the wire-gauze strainer of the pump was a very bad fit in a deep recess, the latter partly filled with the chaff already mentioned. The area of the wire gauze was miserably small, and when filling the oil chamber, the bulk of the oil ran down at the edges, where the strainer did not fit, carrying the accumulation of dirt from the recess with it. Even that was too slow for the driver, who lifted out the strainer and got the reservoir filled faster, with just about. as good a result as if the strainer had been'in position.
Detailed Investigation.
The answer to the second query, ai to why the pump did not force the obstruction through, or burst the pipe, was not so apparent. The next time we heard the cylinders calling for oil, we made a
thorough investigation. The oil-pump was fitted with a glass, where the amount of feed should be seen, but owing to the presence of dirty oil on the inside of the glass, nothing could be there seen. This was taken off and cleaned, and then we found the pump was working, and giving a good supply of oil through the sight glass. We then removed the steam chest cover, and found not a sign of oil ; all was as dry as Sahara! We then worked the pump by hand, and saw the drops passing through the glass, but not a drop came through to the cylinders. We cleared the obstruction from the delivery check valves, and then got a plentiful supply through to the steam chest.
This particular pump was fitted with two plungers ; the first plunger had a variable stroke, to regulate the supply, and it pumped the oil through the sight • glass to the second plunger, which was supposed to drive it home, but there was no means of knowing that it did so.
Leaking Past the Plunger.
The weather was hot— over 160 degrees in the sun—so the oil was hot and thin, and leaked freely past. even a good-fitting plunger, back into the oil chamber again. We found it did this whenever it had to purnn against a moderate pressure. The plunger was only making five strokes per minute, and the wimle suonly was disappearing in this fashion. Could we have worked with cold, thick oil, I have no doubt the pumps would not. have given so much trouble. Why did the drivr not notice that the level of oil was not lowering in •the.chamber ? That is jqat •
where the fool coMes in. How can one'-expect a man to think of such
-7.hings, when he -will not even tighten a. nut which le sees coming off under his very nose.
A File Tang Through a Sight Gauge.
This oil-pump had also what appeared to be a glass, to show the depth of oil in the chamber. This also was fixed in a recess, but so dirty did it become that it was impossible to see the oil level ; so when we were cleaning the sight glass, the driver was told to clean it also. This he did, with a piece of waste stuck on the end of a file tang.
Shortly after this general clean up, the cylinders were again calling out for oil, and upon investigation we found the oil chamber to be empty. We found that the sight hole, in the end of the chamber, was not fitted with glass, but with a. thin sheet of mica, and he had put the file tang through it, leaving a small hole. The oil had leaked out down to the level of this hole, and the pump had finished the remainder before the next filling time. Why did the driver not see the oil running away'? Because he was a foal, and could only work with things " fool-proof."
The Ratchet Overruns.
I began to take an interest in this oil-pump, and I watched it closely. The ratchet was supposed to be taking two teeth for each stroke of the engine, and for some weeks it kept to the contract ; but when it Fat more accustomed to the job, it sometimes acquired a strange habit of taking two, and sometimes three, six, or eight teeth. The engine was running 260 revs, per minute, so the pawl met the teeth with a quick blow. When the plunger was forcing, the pump stuck to the two teeth per stroke, but when there was no pressure to overcome, the wheel simply romped round every time the pawl hit it, without regard to numbers of teeth, and then got to business again at two teeth during the working stroke.
I came home with a virtuous resolution to slay all makers of oil-pumps, but the maker of this pump in particular.
A List of Violets.
When we find out what, won't do, we are a long way towards finding out what will do. By this time I had found out a lot of "won't do" things, and of these the most important were
(a) That pumps set in a cool place won't pump oil in frosty or cold weather.
(b) They won't pump some of the heavy thick oils, which are nearly as plastic as vaseline, unless the oil be hot.
(c) That. if chaff and cotton waste enter the oil chamber along with the oil, the pump won't pump for long.
(d) That if there are any sight glasses about the pump, they won't be there long, and when they are there they won't be cleaned inside.
(e) That if there are any open-mouth cups, or recesses, where the oil is poured in, they won't be cleared of cinders, chaff, etc., before the chamber is recharged with oil.
(f) That a gauze-wire strainer of small area won't take the oil fast enough for the ordinary run of drivers, and it won't be long before it is lifted out when filling.
(g) That an oil-pump fitted with pawl and ratchet wheel of large size, on a high-speed engine, won't stick to its contract of two teeth per rev, of the engine, after everything has worn " free and easy."
(h) Thatthe small valves in oil-pumps will work with any kind of oil, so long as it is hot, but that five pumps out of ten won't pump hot oil against any pressure.
(i) That if instructions concerning oil-pumps are sent out with them, the driver won't read them, for as a. rule he cannot read.
Knowing all these " worets " I commenced to inter-view the victims—the oil-pump men, and I must say I never met a. more astonished lot of innocents. They simply could not believe one word of my tale of woe. They one and all had supplied hundreds to this and that firm, and had never had a complaint—not even a murmur. I remembered that the Bible says something about all men being " perverters of veracity," so I continued my interviews until I found one honest pump-man. He was not a salesman, but the manager of an oil-pump works, and he actually admitted that there might be room for improvement, but not at present prices. However, I was out after a " foolproof" pump, and I had a comfortable feeling that prices might be left for my big brother to wrestle with. once I got what I wanted.
A New Specification.
The pump-man said " make a sketch of what you want, and I will criticize it from a pump-maker's point of view. I made my sketch, and he soon proved to me that he was no fool, but just the man I wanted to make a " fool-proof " pump. My requirements were as follow (a) After I had gone over all my " won't do" things with the pump-man, we agreed that the "
fool-proof" pump must be made to pump hot oil, say up to 200' Fahr. The pump to be fixed directly on the cylinders (see lig, 4), where we had already found it attained an oil temperature of .180° Fahr.
(b) That fluff and chaff or other foreign matter, must be kept out of the oil chamber at all cost.
(c) That the gauze-wire oil strainer should be carried in a brass cage, and be cylindrical in
shape (see A, Figs_ and 2) of large internal diameter, and extend the whole depth of the oil chamber, so as to give ample area of gauze wire for the oil to pass through. The top of this cage to be turned a perfect fit at B, for a hole bored in the top of the oil chamber; round the top of this hole to he a turned spigot (C), covered with a cap (D), fitting externally, and held in place by a bolt and spring (E), arranged to allow the cap to swing clear when filling. The gauze wire (F) to be wrapped round the core of the cage, and cast into it in the brass foundry, the vertical joint of the gauze wire being in the centre of one of the vertical bars of the cage, rendering all soldering or other fixing of the gauze wire unnecessary, the whole arrangement making it impossible for oil to enter the oil chamber, except through the fine mesh of the gauze wire.
The large diameter of this cylinder also admits of easy filling from any kind of vessel. The driver is able to see the depth of oil in the chamber, without taking out the strainer, which is quite usual where the strainer covers the mouth of the filling hole. The whole safety and success of the oil-pump depends on this strainer's always being kept in place, just as the miner's life depends on the gauze wire in his safety lamp. Therefore I felt sorely tempted to specify that it should be padlocked in place like the miner's lamp.
(d) That the eccentric shaft (G) be placed at the highest oil level in the oil chamber, and covered by a lid (El), secured by four bolts to a faced joint made with gauze wire (J), to prevent any dust, which may come through the vent hole (K), getting into the oil chamber.
(e) That the eccentric shaft (G) be fitted with two spiral springs (L1,1), pressing in opposite directions against washer plates (M111), these washer plates in turn pressing against the sines of the eccentric (N), to act. as a slight brake, and prevent the ratchet wheel (0) revolving beyond the point where the pawl (P) leaves it,Ialso to prevent the ratchet. wheels being pulled back by the drag of the pawl (P) when returning.
Tlp-Qe washer plates (3,1) to be anchored by a pin (Q) passing through them at a considerable
radius from the centre of the eccentric shaft, to prevent any circumferential movement of the washer plates. If these washer plates were not anchored, they would give a torsional stress to the springs, causing a recoil every time the pawl left the teeth of the ratchet wheel, which would be fatal to good working when only taking one or two teeth each stroke.
For the same reason the pawl lever (R) is not carried on the eccentric spindle, but on a trunnion (S), cast with the body of the oil-pump, and turned to receive the bored eye of the lever (R). The spindle (G) passes through the centre of trunnion (S), and the reciprocating lever (R) has no disturbing effect on it in either direction. (f) As it is very important to keep the eccentric and washer plates well and constantly oiled, an oil bath (T) is provided under the eccentric, so that it dips in the bath each stroke. Any 'leakage past the plunger (U) maintains the oil level in this bath, the surplus oil dripping back into the oil chamber over the lip of the bath.
(g) The ratchet wheel and pawl were specified to be drop forgings, of ample width of face. The teeth to be accurately machine cut, and afterwards case-hardened.
(h) The pump plunger and crosshead to be a drop forging, turned and ground dead parallel, and a good working fit in the barrel.
After agreeing this specification with the pumpman, it only remained for us to settle the price, which we managed, and we gave him the order for 100 pumps. We then thought our oil-pump troubles were done, but alas, as the next portion of this screed will show, they had only just begun.