Landships II

Jim Lawrie · Corporal

Hydro-Pneumatic vs Hydro-Spring: Practical differences?

CharlieC · Legend

Russian artillerymen in WW1 preferred the hydro-spring system because it was more reliable than the hydro-pneumatic system and

even if it did break (spring breakages weren't uncommon) the system could be fixed at local workshop level. The hydro-pneumatic system

required continuous and ongoing maintenance to keep it working properly. The Russians had the advantage of two 122mm howitzers of nearly

identical performance one from Schneider with hydro-pneumatic and the other from Krupp with hydro-spring.

Charlie

nuyt · Major

Interesting discussion and subject. Were Krupp's weapons mainly hydro-spring by WW1?

CharlieC · Legend

I think you are right - the only gun I can think of which had pneumatic recuperation was the 15cm sFH 13 and that was

a response to problems with recuperator spring breakages.

Another aspect is the cost of production of hydro-pneumatic systems - these required very accurate machining else they didn't work.

There is somewhere on this forum a description of the machining steps the Singer Company used to produce the recoil systems

for the US built Mle 1897 field guns. I'd assert the machining and the cost of a hydro-spring system would have been a small fraction

of the cost of the Mle 1897 hydro-pneumatic recoil/recuperator.

I'd also point out that the Mle 1897 is held up as an example of total recoil absorption and it was, under ideal conditions. Where the ground was water saturated,

even with the wheels locked, the gun would slither back anything up to a meter.

Charlie

nuyt · Major

Thanks, great insights.

CharlieC · Legend

One of the more approachable texts on recoil systems is the 1963 pamphlet produced by the US Army - Recoil Systems Design

https://archive.org/details/DTIC_AD0830281/mode/2up

Charlie

Jim Lawrie · Corporal

From memory the Mle 1897 recoil piston was essentially put together in a craftsman process unlike the rest of the gun. The USA had immense problems machining the tolerances.

CharlieC · Legend

Exactly so - the French machined the receiver to close to the final dimensions with the final fitting done by hand.

Apparently the reason the Singer Co. was chosen for Mle 1897 receiver machining is that they had ahead start in accurate machining from their sewing

machine manufacture. It took many months of development work to produce a satisfactory Mle 1897 receiver in the US - the first US made guns weren't

completed until a few weeks before the Armistice.

Charlie

AN5843 · Sergeant

The Army Ordnance magazine Vol 3-4, from 1922, has 2 articles on the subject. One advocates for hydro-spring, one for hydro-pneumatic. They can be found here:
https://www.google.com/books/edition/Army_Ordnance/trbmAAAAMAAJ?hl=en&gbpv=1&bsq=hydro

on pages 53-54 for the pro-hydrospring article (Spring Return versus Recuperator by J.E. Munroe) and on pages 230-233 for the pro-hydropneumatic article (Advantages of Hydro-Pneumatic Recoil Systems by D.A. Gurney and W.C. Young).

In general hydro-spring recuperators are smaller and lighter for the smaller artillery, and are easier to manufacture and maintain. For larger artillery pieces this falls away and more modern hydro-pneumatic recuperators started to weigh less than hydro-spring recuperators even for lighter guns (this is shown in the second article). On the production of hydro-pneumatic recoil systems, when Singer tried to manufacture recuperators for the Canon de 75, they initially wanted to train people to lap the recoil cylinders by hand, just like the French did. But they had no time to train people to lap the cylinders, the guns were needed as fast as possible. One of my previous series of posts describes this:

The real trouble began at operation 42 which was the lapping of the small cylinder. Two thousandths of an inch had been allowed for this lap ping and proved to be sufficient to remove the tool marks of the finish-reaming. It was originally thought that it would not be possible to do this lapping entirely in a mechanical way and that a considerable time would be required to instruct and train men in the art of lapping. However, it was not thought practical to attempt to train men to a point where, by the mere skill of hands and eye, they would be able to produce both the extreme accuracy required and the beautiful finish which was said to be necessary.

The following method was adopted and proved to be entirely satisfactory for producing holes of the proper finish and of much higher accuracy than required in the specifications. It is believed that the success with the recoil mechanism as manufactured by the Singer Manufacturing Co. was largely, if not entirely, due to this method of lapping.

So the limitation of hydro-pneumatic recoil systems in WW1 was not directly in production costs, but in the ability to ramp up production (limited by the time required to train people to lap cylinders to high accuracy).

The main benefit of hydro-pneumatic recuperators was their longer lifespan, and their smaller size and weight for larger guns as well. The second article I mentioned from Army Ordnance states:

It is fairly well established that the French 75-mm. mechanism may be expected to stand up for 20,000 rounds without any major difficulty, and some have been fired a greater number of rounds without overhaul. It is very doubtful if any hydro-spring mechanism would endure more than 5,000 rounds without replacement of springs. Breakage of springs is a very frequent occurrence. For example, recently in a short target practice of 75-mm. guns, Model 1917 (British), 75 per cent of the springs in the battery broke during that practice.

It is interesting to note the results met with in the use of the 18-pdr. gun carriage, Model 1917 (British), during the World War. The replacement of springs ran to a rather high percentage. From the observation of a considerable number of carriages under these war conditions the replacements of springs required were very considerable. Assuming the life of the 75-mm. gun to be about 14,000 rounds, reports indicate that during the life of every four guns over 200 springs required replacement.

In most nations that lifespan was decisive, so once production difficulties with hydropneumatic recuperators were solved (either with direct-contact hydropneumatic recuperators, which didn't need such precision, or with advanced machining technology for floating-piston hydropneumatic recuperators) they became the standard. For Britain, this happened around 1916 with direct-contact recuperators, and around 1918 with floating-piston recuperators. The one exception is tanks- they apparently use chydro-spring recoil systems (concentric recoil mechanisms) to this day, according to the Recoil Systems Handbook (page 42). This is because of their smaller size and lower weight, and the fact that tanks are not likely to fire that many rounds compared to an artillery piece (this does mean that tanks used as mobile artillery during war will wear out their guns faster than dedicated self-propelled artillery guns will).