What Is the Difference Between a Hydraulic and A Pneumatic Cylinder?
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What Is the Difference Between a Hydraulic and A Pneumatic Cylinder?
A mechanical actuator, a hydraulic cylinder, employs pressurized hydraulic fluid to produce force in a linear motion. It is utilized in various applications that require strong force output and precise motion control.
A pneumatic cylinder is a mechanical actuator that transforms compressed air energy into linear motion. Mostly, they are renowned for their sturdiness, low maintenance requirements and excellent efficiency.
Usage
Both cylinders are frequently seen in heavy-duty vehicles like cranes, excavators, industrial machines, and construction equipment.
They are also employed in construction machinery like bulldozers, excavators, and cranes for lifting and moving massive objects.
Hydraulic cylinder
Common characteristics of pneumatic and hydraulic cylinders
Pneumatic and hydraulic cylinders are made to bear enormous weights and high pressure.
They can function in a variety of temperatures and weather conditions.
The cylinders can be modified to fulfil particular needs, including various stroke lengths, mounting arrangements and end fittings.
Pneumatic cylinder
Significant differences between the hydraulic and pneumatic cylinder
Source of power:The source of power determines how hydraulic and pneumatic cylinders differ. Pneumatic cylinders use compressed air to create the force, whereas hydraulic cylinders use a liquid, usually oil, as the fluid medium.
Force production:Pneumatic cylinders cannot produce as much force as hydraulic cylinders. Because liquids are practically incompressible, they may produce strong force even at low speeds in hydraulic cylinders. On the other hand, pneumatic cylinders can produce less force because air is easily compressed.
Precision:Compared to hydraulic cylinders, pneumatic cylinders have a higher operating speed. Since the air is compressible, it allows for more rapid acceleration and deceleration. However, hydraulic cylinders can only function at slower rates due to the fluid's viscosity.
Precision:Pneumatic cylinders are frequently less precise than hydraulic cylinders. This is due to the non-compressibility of hydraulic fluid, which enables accurate control of motion and position. On the other hand, fluctuations in air pressure and temperature impact the pneumatic cylinder resulting in less precise performance.
In general, pneumatic cylinders require less upkeep than hydraulic cylinders. This allows compressed air to be easily obtained, produced, and filtered with less equipment. Conversely, replacing hydraulic fluid can be more expensive and requires additional filtering and conditioning equipment.
In applications where speed of operation is crucial, cost-effectiveness is a top concern, and the needed force is relatively low, pneumatic cylinders are typically favored over hydraulic cylinders.
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Hydraulic or Pneumatic Cylinder as a Liquid Pump?
thread404-438740 Forum Search FAQs Links MVPsForum
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(Mechanical)
(OP)
8 May 18 14:57Hi all,
I need to replace a plastic 3ml syringe on an experimental setup to something more robust.
The syringe acts as a miniature pump, and the pumping action is at a very high frequancy which results in leakeges of air in to the system.
The substance that the syringe is pumping is water mixed with glicerol.
I was wondering if a small pneumatic cylinder will do the job, or I have to find an hydraulic cylinder that can handle liquids less viscous than oil?
The reason I'm asking is that I have little experience with hydraulic and pneumatic cylinders.
(Mechanical)
8 May 18 15:08It might work for a while.If you need a pump why don't you use......an actual pump?Perhaps https://en.wikipedia.org/wiki/Peristaltic_pump Or http://www.micropump.ca/ Or something else from the entire universe of products that are actually intended to do what you need to do.
(Mechanical)
(OP)
8 May 18 15:19A regular pump wont do the job in the parameters we need it to work.
The system setup is a closed loop, and the syringe is reciprocating the liquid back and forth, at very high frequency of up to 5Hz.
(Mechanical)
8 May 18 15:53A diaphragm pump might do a better job at those frequencies. No sliding seal is going to not allow some air to slip through (unless your system pressure was higher than the amplitude of dynamic pressure at the piston face). I'd think a piezo driver immersed in your fluid would give a better frequency response than a syringe - are you actually seeing that frequency at points in the system distant from the "pump"?
(Mechanical)
8 May 18 16:02When you say "the system is a closed loop" do you mean you have the same fluid on both sides of the piston, and you're actually oscillating flow?
Depending on your fluid, you might be able to build a linear peristaltic pump that would create oscillating flow. The key variable would be whether or not there is a tube material which is flexible enough to use in a peristaltic pump and compatible with your fluid.
This pump would consist of a length of compatible tubing, a few machined parts, a linear actuator (either mechanical or pneumatic) and the controls for said actuator. Which you may already have, to drive this syringe arrangement.
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(Mechanical)
8 May 18 16:06Bellows syringe ?
(Mechanical)
(OP)
8 May 18 17:43Any type of pump is out of the question, the actuation is precisely controlled by an actuator with precisely tuned pumping profiles.Quote (btrueblood)
A diaphragm pump might do a better job at those frequencies. No sliding seal is going to not allow some air to slip through (unless your system pressure was higher than the amplitude of dynamic pressure at the piston face). I'd think a piezo driver immersed in your fluid would give a better frequency response than a syringe
Yes, the loop is very small.Quote (btrueblood)
are you actually seeing that frequency at points in the system distant from the "pump"?
With the syringe, there are a set of valves which directs the flow; reservoir->syringe->lung model->reservoir.Quote (jgKRI)
When you say "the system is a closed loop" do you mean you have the same fluid on both sides of the piston, and you're actually oscillating flow?
Thanks, wasn't aware of this type of syringes.Quote (rothers)
Bellows syringe ?
Any type of pump is out of the question, the actuation is precisely controlled by an actuator with precisely tuned pumping profiles.And yes,Yes, the loop is very small.It consists of a small reservoir, optical silicone model of an infant lung air ways and the syringe-actuator assembly.With the syringe, there are a set of valves which directs the flow; reservoir->syringe->lung model->reservoir.In case of a double acting cylinder, the system fluid lines can be easily rearranged.Thanks, wasn't aware of this type of syringes.
(Industrial)
8 May 18 18:25Piston or Plunger pump with the check valve(s) removed to just move the fluid back and forth?
(Mechanical)
8 May 18 18:30Helepolis,Is a syringe going to operate reliably for any length of time at 5Hz? Do nurses and physicians with syringes operate at 5Hz?
--
JHG
(Mechanical)
9 May 18 14:40Sorry, I thought I read 5 kHz and was wondering why in the heck you'd be beeping noise into an infant's lungs. Even 5 Hz seems way to high a frequency, unless you are just pushing to get some kind of cycle testing done?
"Any type of pump is out of the question" -- no. Your syringes are a type of pump too, the way you are using them. So "some" type of pump is apparently acceptable, but you aren't saying much about why. You mentioned valves directing flow, which is what check valves in a plunger pump would also do. If you want to control the valves yourself, fine. Still a pump.
I think a diaphragm (pump) is still the right way to go. You can drive a diaphragm with an actuator as easily as a cylinder. A bellows syringe would work too, as would a rolling diaphragm cylinder. If air entrainment is a problem for you, then you need to design out any sliding seals, imo.
(Industrial)
9 May 18 16:44Wow, I was sure it was 5kHz, too. I guess when I saw "very high frequency" my mind just jumped to kHz.
(Mechanical)
9 May 18 17:07btrueblood,I was thinking 5kHz too, but I re-read the OP.
--
JHG
(Mechanical)
9 May 18 17:12It occurs to me that you could use something like the peristaltic pump mentioned, only don't make full revolutions with it- just back and forth in a 90 degree arc or so.
(Mechanical)
9 May 18 18:12Yeah, but I just don't like the fatigue issues with peristaltic pumps so usually don't consider them. For lab testing it's probably a pretty good idea, though. And tubing is fairly cheap, and controls for stepper motors to drive the pump likewise common and fairly cheap. Presumably there is some type of waveform modulation going on requiring a 5hz capability, and that's quickly achievable with that setup.
(Mechanical)
(OP)
9 May 18 18:14Thanks, I'll look into that.Quote (John2024)
Piston or Plunger pump with the check valve(s) removed to just move the fluid back and forth?
I'm guessing that it wont hold up its integrity for long, but i don't care.Quote (drawoh)
Is a syringe going to operate reliably for any length of time at 5Hz? Do nurses and physicians with syringes operate at 5Hz?
I meant that i can't use any commercially available pump, as the setup uses a very precise magnetic linear actuator, so i need to work with it.Quote (btrueblood)
"Any type of pump is out of the question" -- no. Your syringes are a type of pump too, the way you are using them. So "some" type of pump is apparently acceptable
Quote (John2024)
Wow, I was sure it was 5kHz, too. I guess when I saw "very high frequency" my mind just jumped to kHz.
Yeah, i shouldn't have written "very high" when it lacks context, but when it concerns ventilating preterm birth, 5Hz is a lot (Quote (drawoh)
btrueblood,
I was thinking 5kHz too, but I re-read the OP.
Can a peristaltic pump operate at 5Hz?Quote (JStephen)
It occurs to me that you could use something like the peristaltic pump mentioned, only don't make full revolutions with it- just back and forth in a 90 degree arc or so.
Thanks, I'll look into that.I'm guessing that it wont hold up its integrity for long, but i don't care.This setup is meant to simulate the flow field of HFOV - High Frequency Oscillation Ventilation.Once everything is running as it should, the flow will be imaged using a method called TomoPIV, where an output of 4 high speed,strategically placed, cameras is combined into a 3D flow filed.So i need no more than a couple of seconds of operation to capture the flow.I meant that i can't use any commercially available pump, as the setup uses a very precise magnetic linear actuator, so i need to work with it.The high precision is paramount for the experiment, the total transported volume is about 1.5-2 ml of liquid at high speeds and the actuator delivers exactly that.And if, i will be able to find a compact, high precision, low volume, high frequency oscillating pump it'll probably cost way to much.Yeah, i shouldn't have written "very high" when it lacks context, but when it concerns ventilating preterm birth, 5Hz is a lot ( link Can a peristaltic pump operate at 5Hz?
(Mechanical)
9 May 18 18:33Set up two bladders, hydraulically one on either side of the component, totally sealed system. Drive a lever arm so when one side goes up, the other goes down, and presses on a bladder. Use a small % of the bladder capacity as the working volume to avoid fatigue problems. When you press down on one, it refills the other.
Drive system could be as simple or complicated as you want, using up/down lever mostly just to illustrate the concept. Pneumatic, linear actuator, rotating cam, reciprocating piston, etc.
For that small volume, you could probably just squish some rubber tubing, the bladder is mostly conceptual.
(Chemical)
9 May 18 19:38A diaphragm pump with check valves will do this well.
A piston/plunger pump with check valves removed will also do this very well.
A syringe pump also exists, but will not like running at 5 Hz forward/backward.
(Mechanical)
10 May 18 14:56"Can a peristaltic pump operate at 5Hz?"
Yes. Finding one off the shelf to do that is probably going to be tricky. I'd purpose build one to do it with a stepper motor and controller, and a bit of software. But you have to use a linear actuator, so what's the point of asking?
(Mechanical)
12 May 18 21:43This post has gone from answering the original question to suggestions on how to solve this with other mechanical devices or pumps.On use of cylinder built for air in general: I have successful (and with permit from the producer) used pure water directly to operate air cylinders of aluminium. Answer: a standard air cylinder built for normal pneumatic pressure, and with parts compatible with water/glycol will in general function.Quite another question is if you will find one cylinder on the commercial market that will suit and function within your requirements.What is the size and size restrictions? How does it operate? Suck in as a syringe in a single stroke, and pump out in one longstroke or several smaller? Or another way? One way in (port one) and anotherway out (port two). Time limits in the sequence?More information is necessary for design. Checking the internet: cylinders with 5 mm cylinder boring seems to be about the smallest available? Too large?Good Luck!
(Mechanical)
14 May 18 16:42Hope I'm not too late to the party.You could possibly get away without making many changes at all. If the problem is only that you are getting leakages of air into the system, simply rearrange your existing setup such that the syringe is arranged vertically and then simply fill the back side of the syringe cavity with your working fluid. If you get any leakage, then what is leaking in and out is the same working fluid you are already using. Or leave the syringe horizontal and use silicone to mold a case to keep the entire pumping end submerged in your working fluid. Or if you want to be really cheap and clever, use tape and a plastic bag. I like cheap and clever.Second alternative is to machine a new plunger out of UHMW or aluminum and put 2-3 seal grooves and seals in it. Assemble the barrel and plunger submerged in the working fluid and you should be able to prevent any fluid from passing out of or into your loop.
Engineering is not the science behind building. It is the science behind not building.
(Mechanical)
14 May 18 17:14Go to a company that makes pumps for that purpose! There are several different companies that make pumps of all types (rotary, piston, diaphragm, rolling, etc.) specifically for laboratory operations and for all types of liquid media.
(Electrical)
15 May 18 03:36This application is similar on a much bigger scaleThere were two diaphragm pumps pumping fuel into a diesel engine. There were two hydraulic cylinder pushing the diaphragm pumps. The goal was to keep the pressure constant. The problem was that the hydraulic designer screwed it all up and didn't consider many things.To keep the pressure constant one pump had to be going forward as the other was retracting. It was a little trickier than that because the fuel compressed so much. The pumps had to move forward about 30% of stroke because the fuel had to be pressurized to 40,000+ psi before the check valve would open up. This meant that there should have been times when both pumps were moving forward but the hydraulic designer didn't allow the pump to retract fast enough so there was some ripple.Just scale this down to milliliters.The OP said nothing about keeping the pressure or flow constant. Is this important?5HZ is nothing.
Peter Nachtwey
Delta Computer Systems
http://www.deltamotion.com
http://forum.deltamotion.com/
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