Hydraulic cylinder question

mellotango

Hi,

I posed some questions regarding the use of hydraulics before in this forum, and this time I would like to know if it is technically possible to use refrigerants or steam to drive a hydraulic cylinder. It's part of an organic rankine energy generation project I'm hoping to attempt. I have been previously offered suggestions to use air cylinders, air motors, centrifugal pumps, turbo expanders etc for such a purpose. However, I am only specifically interested just to know whether it is possible to use hydraulic cylinders driven by refrigerants or steam. Part of the reason is hydraulic cylinders are able to handle much more pressure than air cylinders, which can handle maximum of 150 psi. The pressure I am looking at could be as high as 300 psi or more. So instead of having to custom make an air cylinder to handle those pressure, why not simply use a hydraulic cylinder which can handle the pressures easily? Would there be problems of friction, leakage or corrosion? So far I have found no evidence that says that this cannot be done. Hence, I am looking for some opinion here as to whether it is doable. If it is indeed possible, I would also like to know what kind of lubricants (if needed at all) is suitable for this type of usage as well as how much and how often to apply. Any tips on this would be appreciated. Thx in advance.

KrizG

I believe this would be possible. There are a few possible problems I can think of. Slight leakage (because you are working gaseous substances) could be an issue. Also, the strength of any pipes, valves, etc. that you are using may be lower than the strength of the cylinders. There may also be some contamination from lubricants; (I think some sort of lubricant would be required if you want it to operate at high speed/temperature).

256bits

Hydraulic fluids are used for a simple reason in that they can be considered incompressible in the application.

Have you considered what would happen to the pressure in your hydraulic cylinder as the steam begins to cool and condenses into water. would you still have pressure then?

mellotango

I'm glad so far no one has told me that it cannot be done, so the idea still seems promising. As for steam, perhaps it may have to be in the form of semi superheated steam so little condensation occurs even as it exits the outlet. This will have to be experimented upon. Same goes for refrigerants, and it may behave better than steam as it will probably condense at much lower ambient air temperatures. But wouldn't controlling the entry steam/refrigerant flow rate ensure there would be enough gas for expansion to maintain the pressure? Also, my other main concern would be whether these types of working fluid will cause any type of fouling in the cylinder over the long term. Any inputs on this? And for possible gas leakage, there are rodless type hydraulic cylinders which are supposedly tightly sealed and may help to minimise leakage as there are no outer pistons involved. So that's something to consider too.

malemdk

The sealing elements hydraulic cylinders meant for hydraulic oil ,these are specifically selected and designed and not for steam or refrigerant

pantaz

Have you considered the reasons for limiting the pneumatic pressure?

In theory, sure, it's simply fluid pressure (be it pneumatic or hydraulic) acting on a piston. In actual practice, I have many doubts. I imagine you could get it to function, but it would almost certainly be dangerous and prone to failure.

Unless you can find someone that has already built a similar system, lubrication is going to be guesswork. A properly qualified engineer could likely recommend something given the temperatures, pressures, and materials.

I can only imagine the difficulties in dealing with temperature control throughout the system.

You should investigate the thermodynamic properties of refrigerants.

It's certainly possible, since you're putting materials into machines that were not designed to use them.

"Tightly sealed" doesn't mean much if the seal material is incompatible with the pressure and/or temperature and/or fluid.

mellotango

Pantaz,

I'm guessing the reason for limiting pneumatic pressure is because most standard air tools, and hence majority of air compressors work at a range of about 90 psi. Therefore pneumatic cylinders and motors are manufactured to match the pressure of range of common air compressors. Plus, they are made of lighter materials to lower costs.

As for the properties of refrigerants, this is what I've been looking at. http://webbook.nist.gov/chemistry/fluid/

I'll be heading down to suppliers for pneumatic/hydraulic components next week to get more info with them. Will keep this forum informed.

Thx

pantaz

Not even remotely correct. You have a lot more research to do before designing a fluid power system -- let alone some weird hybrid!

mellotango

I think I have made the point before that I do know air cylinders are limited to 150 psi, simply because the materials are not made of anything stronger to withstand higher pressures. And it think it is clearly obvious to anyone that this means using any higher pressure will pose dangers to safety in doing so. But I'm adding to the fact that most air tools in the industry are in the range of 90 psi which means air cylinders are manufactured to cater for this common pressure range for most applications. But since my application is different and involves the use of higher pressure gas, I'm just researching the possibilities of using a hydraulic cylinder instead, since they are built to withstand thousands of psi pressure. And I am trying to find more research help through this forum, in addition to the amounts of research I have already done with regards to organic rankine.

So far, your replies have not been very useful either, sorry to be blunt. Replies like


"Have you considered the reasons for limiting the pneumatic pressure?..."

"In actual practice, I have many doubts. I imagine you could get it to function..."

"I can only imagine the difficulties in dealing with temperature control..."

"You should investigate the thermodynamic properties of refrigerants..."


do not amount to much in terms of expert opinion. For example, in your last reply, you mentioned my theory is not remotely right. So why don't you explain what the real answer or reasons may be? Some of us may learn something from you. Don't get me wrong, all types of viewpoints are welcome with regards to this project (if at all feasible). But if one is going to be an active naysayer, pls at least back it up with some expert statements. When you do, myself and other readers in this forum may actually respect your views and take your word for it.

What constitutes weird hybrid to you, may one day allow those interested in creating small scale clean energy to use immediate, cheap, readily available off-the-shelf industrial components without resorting to costly laboratory prototyping.

pantaz

The last air cylinders I used were rated for 250 psi.

Components designed for higher pressures cost more to produce. It's quite common for a manufacturer to offer the same basic item in a variety of cost/capability levels. So, someone building a system that will never exceed 100 psi, for example, can save money by purchasing components rated for lower pressure.

In the case of a component/system rated for a specific maximum working pressure, yes. However, properly designed pneumatic systems can use much higher pressures. For example, Makita Tools offers a 400 psi compressor and nail guns operating at 320 psi.

There is no correlation between the operating pressure of air tools (impact wrench, air drill, etc.) and the maximum pressure of a pneumatic cylinder or actuator.

I would use that high pressure gas to power a hydraulic pump or air compressor, then operate a conventional hydraulic or pneumatic system. Also, doesn't the Rankine cycle require a closed system? Pneumatics operate as a total-loss system. Air is exhausted to the atmosphere after doing its work.

I've been trying to nudge you into properly researching your project. When you take an established technology (hydraulics/pneumatics) and modify it with untried methods, there are risks involved. When you're dealing with high pressure gasses and fluids, those risks can reach life threatening potential. This is not a subject to take shortcuts with.

You want to mix liquids and gases to operate hydraulic cylinders in a "pneumatic" system. I feel pretty safe calling it a weird hybrid. (Yes, there is a class of "common" hybrid -- see, air over hydraulic.)

This thread has covered potential issues with seals, lubrication, corrosion; you're already moving away from off-the-shelf availability.

How does this relate to "creating small scale clean energy"?

mellotango

When I mention off-the-shelf components and small scale clean energy generation, what I mean is to use common industrial components with minimal modifications, be it air-over-hydraulic intensifiers, air/hydraulic motors, reverse flow centrifugal pumps, etc to generate rotary power to drive a small generator. And in this case, we are dealing with waste steam or waste heat (orc). I have already identified similar success attempts by people on the web for such projects, so that's where we're hoping to get some inspiration from. Of course, maximum efficiency will be something to be traded off with.

I do understand the dangers of attempting something blindly, especially with steam or pressured gas, which is why I'm trying to do as much homework as possible. It will still be a little more time before we go shopping for parts, and putting a working model together. We're only looking to build a small system to start with. I will also take the suggested route to see if suppliers could custom make a pneumatic/hydraulic component for our application. But I doubt it will be easy as most of our local suppliers deal with selling of standard imported components only.

As for a rankine system, you are right it needs to be closed loop. And we aim to make it this way by recovering exhausted gas and condensing it back. The in/out gas into the cylinders will be controlled via solenoid valves or 3-way valves, of which the mechanics of this system is still in the works not quite relevant in this thread atm. We have also worked out the specs for the required plate evaporator, condenser, working fluid pump, etc for rated horsepower output that we need.

Nihilist

What is the rest of the reason for considering hydraulics when you intend on working with gas?

beaufountain

Hello,

I'm working on something that requires a hydraulic cylinder to pull from an extended position and curious if there is any power loss pulling vs pushing??