Pneumatic Cylinders in Parallel

It is always preferable to have a single cylinder where possible. Two cylinders are more difficult to accurately control even when the die plate is supported by bearings at each end.

The two 3" (approx) cylinders will exert a combined force of approx 720 lbf (sorry I still work in imperial sizes, you young spuds can re-calculate). One 4" bore cylinder will exert the same force, be cheaper than two and save you control problems.

One 100mm cylinder will give you the same pressure. Most of my dies are hydraulic. Use a SAE flange mount, mounted to top of die rod going through and attached to lower die plate with adapter. Adaptor adjust how far stoke comes down. Have a few pneumatic set up is the same. Cylinder lifts die open no springs

Thanks for the inputs guys! I do agree with you that one cylinder would be preferred, however, the two cylinders are already existing (as well as valves, etc.), as such I do not want to spend for a new cylinder.

Hi Solrac

"the two cylinders are already existing" was not clear initially.

You need to decide if you actually do need the two cylinders to perform the operation. This is the force required to complete the operation and is the result of the cylinder full bore area x the pressure (air).

Assuming that you have decided that this is necessary, then you need to split the incoming air supply into two equal pipe/hose runs into the cylinders. If the cylinders are double acting you need to do the same with the rod (Annulus) end. The difficulty may lie in controlling the symultaneous downward & retraction stroke of the rams. If the platten that they are fitted to is a fixed slide with bearings then this should not be a problem. If in practice you find that one ram is moving ahead of the other you will need to throttle the output of the leader using flow control (needle) with by pass valves. You may find that even with this mod, temperature changes may affect the air flow, so precise control will still be difficult, but trial and error should give you the best result.

By the way, have you tried fitting just the one ram?

We had to deal with several chronic quality issues due to trying to keep the two cylinders solution in production. It seemed like there were continual adjustments and scrap. We had tried a couple diffenernt guidance solutions, but it all came back to having the EXACT same force being transmitted through each cylinder and each cylinder moving at the EXACT same velocity.

All of our issues that had an "unequal pressure" root cause, were resolved upon changing to a larger single cylinder. In my application, we changed from two 8" cylinders to one 10" cylinder and the mold foot print was about the size of an automobile. If equal pressure is a critical, it may be worth digging a little deeper into going with a single cylinder solution to avoid future quality issues (scrap, scrap, scrap and potientially bad parts going to customers, all which can help justify a single cylinder solution).

This is sound advice.You have summed up in practice what I have been saying in theory. Ditch the two rams and buy one and save a lot of time and effort. Cheaper in the not so long run.

If the die is moving freely you could try disconecting one cylinder, and raising the air pressure in the remaining cylinder till performance is acceptable. You would still be better off with one large cylinder at lower pressure.

Logically at2 diagonal corners of Die.

Another solution is mount the 2 cylinders very close together, on the same mounting, as if they were 1

I have used up to 4 pneumatic cylinders to position die plates with linear bearings without problems for over 20 years. Just make sure to have a valve with sufficient flow and use oversize tubing.

Because of the infinite compressibility of air, the cylinders will equalize force since they are rigidly mounted there is no problem of one advancing quicker than the other.

I have used multiple cylinders in applications where a larger bore cylinder would not fit.

Also on Scissor Lifts, cranes, dumpers and what all.

And for all the Naysayers out there, perhaps they should go look at some construction equipment where almost every movement uses a pair of cylinders. Without problems!

Dear,

Regarding pneumatic cylinder pairing you have to use flow dividers or synchroniser shafting.In flow dividers efficiency is only 90percentage.So it is better to use hydro pneumatic cylinders.

sankar

Perhaps some people should open a book on Fluid Power and review the basics.

The pressure in any any pressurized system is the same on all surfaces of the system.

That includes the piping from the pump, the valve, the hoses going to the cylinder and the cylinder itself. Now, pressure drops can be seen across fittings and through valves depending on the flow of the fluid media and pressure.

Two cylinders seeing the same flow and pressure will advance at the same rate with minor fluctuations due to differences in the friction of the seals. When the two cylinders are tied together they will see the same pressure at the piston end as they advance. I have demonstrated this in Fluid Power Classes I have given by putting "T" fittings in the cylinder ports and fitting gauges to both cylinders. But of course I had equal fittings and hose length going to each cylinder from a "T" on the valve, (which was sized to be able to deliver the needed flow with minimum pressure drop.)

I cannot fathom the difficulties people have with multiple cylinders, multiple motors is a totally different thing but cylinders are not a problem. Large presses have been using multiple cylinders to advance and retract platens for over 70 years. Do a Google search for Presses and go look at them.

Remember, there are a bunch of Engineers who will tell you Bumble Bees cannot fly!

Hi prbarry,

"Perhaps some people should open a book on Fluid Power and review the basics."

Nobody is going to challenge the theory and you may have demonstrated this to good effect in class, but in my 40 years practicle experience in the industry, I do assure you that in virtually every case where I have used multiple cylinders, the rods will extend at different times unless they are fixed together and supported by bearing slides. Even with flow dividers, as has been previously said, the balance is not precise.

This experience has led me to fall back on the use, wherever practicable, of just the one cylinder to save ongoing problems where precision location is required in particular. This has also led to reduced cost in parts and labour during installation.

As you rightly point out, motor circuits are even worse.