very low pressure hydraulics- do they exist?
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  1. #1
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    Default very low pressure hydraulics- do they exist?

    I need to develop a couple little gizmos for one of my products.... and air pretty much sucks at some things , this is going to be one of them, but all I really need is compressed air pressures. I just don't want the compressability of pnuematics, the build and shoot phenomenon is what I am trying to avoid. I have nver been overly impressed with air over oil ( plus the building I'd like to test in has no compressor right now ).

    I could almost use water and a " sprinkler booster pump ", but not sure how reliable that would be..... I think they use water for fluid in some applications. 100 psi would be plenty, low force I just want it to not be able to build pressure and rocket.

    This will also include some control relays, probably a plc, in my grandest dreams a vibratory bowl...... but it starts with the fluid power.

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    in a sense yes, it's how things like self winding garden hoses work. but from what you describe, mechanical systems (screws and the like) may make more sense...

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    There is an elevator in a building I once worked in that ran entirely on "town water pressure".
    50psi and it would lift or lower as much as you could put in the box. I used it hundreds of times.

    The electrical switch gear got to be a head ache however (age). The mechanism is now regulated to "freight only" service. But not due to any failing of the hydraulic design.

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    A starting point. Several references down near the bottom. It's apparently a known technology, but still sounds like higher pressure.

    Low-pressure water hydraulics makes its move | Seals content from Hydraulics & Pneumatics

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    Quote Originally Posted by WILLEO6709 View Post
    I need to develop a couple little gizmos for one of my products.... and air pretty much sucks at some things , this is going to be one of them, but all I really need is compressed air pressures. I just don't want the compressability of pnuematics, the build and shoot phenomenon is what I am trying to avoid. I have nver been overly impressed with air over oil ( plus the building I'd like to test in has no compressor right now ).

    I could almost use water and a " sprinkler booster pump ", but not sure how reliable that would be..... I think they use water for fluid in some applications. 100 psi would be plenty, low force I just want it to not be able to build pressure and rocket.

    This will also include some control relays, probably a plc, in my grandest dreams a vibratory bowl...... but it starts with the fluid power.
    Sounds like you have bad experience with pneumatics... with the correct cylinders/clamps and proper application of regulators, speed control, solenoids what have you... they act very predictably, rapidly, consistently, with power nowadays approaching small hydraulics (via air-mechanical clamps, where such power is required).

    the possibility of using low pressure water, or a small electrically boosted water pressure system could be viable depending what you're actually looking to do.

    what kind of flow-rates do you need for the system? what sort of transmission is going on?

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    I am not going to say exactly what I am looking to do, not going to happen. It will be low flow but moderate speed.

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    Might be worth looking into automotive engine oil pumps and similar. As I understand it most become very inefficient at much above rated pressure and simply leak back. Whether anything suitable will stand up to water rather than oil is a different matter. Interlocking lobe pumps Roots et al style can be easy to make and are self limiting in pressure output. Might not be enough for you.

    Clive

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    Quote Originally Posted by WILLEO6709 View Post
    I need to develop a couple little gizmos for one of my products.... and air pretty much sucks at some things , this is going to be one of them, but all I really need is compressed air pressures. I just don't want the compressability of pnuematics, the build and shoot phenomenon is what I am trying to avoid. I have nver been overly impressed with air over oil ( plus the building I'd like to test in has no compressor right now ).

    I could almost use water and a " sprinkler booster pump ", but not sure how reliable that would be..... I think they use water for fluid in some applications. 100 psi would be plenty, low force I just want it to not be able to build pressure and rocket.

    This will also include some control relays, probably a plc, in my grandest dreams a vibratory bowl...... but it starts with the fluid power.
    Water not. Nuisance keeping it from attacking stuff, growing stuff, freezing, boiling, or some combination thereof.

    An alcohol or glycol, maybe even glycerine?

    Or one of the less-toxic glycols as used for RV toilet anti-freeze, for example. PEG IIRC is even used to preserve museum displays of old wooden artifacts.

    Probably NOT rather nastier Ethylene Glycol anti-freeze, nor most brake fluids.

    Given seals that are compatible, those might work with stock cylinders, lines, and valves made for either air or oilier hydraulic fluids, reducing DIY time and costs.

    Intentionally UNDER driven diaphragm or peristaltic roller pump might be a fit for 'low' pressure & infrequent maintenance, especially with an accumulator for smoothing.

    At higher 'low' pressures, automotive fuel pump and ABS pumps perhaps better examples than automotive oil pumps. Carbureted days, mechanicals lasted long enough and were under 10 PSIG.

    Fuel-injection era saw electric ones arrive, pressures in the 15-20 range, then also over 40 PSIG.
    ABS unit are higher pressure yet, AFAIK. Power steering pumps all over the lot, as are fuel 'transfer' pumps, Bass boat to B-36 bomber.

    The concepts of several are proven sound enough, the goods are cheap and common enough, even if capacity has to be scaled to suit your needs.

    Parts-bin & remainderman/salvager exercise? Frees you to concentrate on DIY of such bits as you cannot as easily purchase.

    Bill

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    I caution you against going this route, as a maintenance tech i have been called on to try and repair odd setups like this before. Can spiral into a night mare of unreliability in just a few years use. Fluid and seal compatibility is a night mare, waters the worst imaginable option, it does not lubricate and causes corrosion + microbial growth.

    Running hydraulics at bellow normal pressures cause all sorts of premature seal failures, most hydraulics need a good few bar of pressure to energise the seals. Equally most need a minimum of 50+ bar for valves to work correctly as designed.

    Fittings can be a major issue too, pneumatic fittings whilst rated at the pressures your discussing often down work well with fluids, sudden water hammer - hydraulic shocks cause issues, issues that you just don't see in pneumatic systems.

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    Quote Originally Posted by adama View Post
    Running hydraulics at bellow normal pressures cause all sorts of premature seal failures, most hydraulics need a good few bar of pressure to energise the seals. Equally most need a minimum of 50+ bar for valves to work correctly as designed.
    True as to what we are most familiar with in 'most' of our shops.

    But there is another source of experience, too.

    The medical equipment field. Human body doesn't take high Bar pressures very well.

    Yes, it is nearly all based around aqueous solutions.

    Even so, a change in seal material should be all as is needed for valves and other bits of kit to Just Work with - for one example only, and perhaps not the best one at that - Glycerine as working fluid.

    Bill

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    Instead of speculating on adaption of high pressure hydraulics, why not just talk to the people that are in the low pressure hydraulic business? They might have some insight on very low pressure systems.

    This link has a listing of components by manufacturers and much information on system design and water requirements. I'd start here:
    http://www.jfpa.biz/wp-content/uploads/ADS_EN2.pdf

    Here are some websites.

    Water-filled hydraulic cylinders | 3A Industrie

    Water hydraulic systems | Hytar

    Water Hydraulics – Pumps, Motors, Cylinders, Valves Datasheets

    Welcome to the web site of Tiefenbach Water Hydraulics Inc. - valve, press and consultant specialists



    Some research papers:
    https://www.jstage.jst.go.jp/article...999_4_357/_pdf

    http://www.jfps.jp/proceedings/tukub...pdf/key_02.pdf

    http://proceedings.asmedigitalcollec...icleid=1599045

    http://www.sv-jme.eu/data/upload/201...688_Liu_03.pdf

    http://journals.sagepub.com/doi/abs/...65180221600502

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    25 yrs ago I built a few drill units that I used hydraulic checking on, to regulate the feed/speed.

    I just put a hydro flow control on the front port of an air cyl, and then up to a larger pipe/resevoir that would hold 2x what the cyl would, and then it was all air beyond that point. Fill the front half with fluid and down the road you go. Works great!

    I guess I never tried it, and maybe Adama is right, but I'd at least try shutting the regulator down to 150/200 and give it a shot on reg hydro products. I have one bank of machines that actually runs at 400psi. Also - when we shut down the pressure on our lathe chucks, sometimes we get down in the 250psi range I think.


    ----------------------------

    Think Snow Eh!
    Ox

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    Quote Originally Posted by Ox View Post
    25 yrs ago I built a few drill units that I used hydraulic checking on, to regulate the feed/speed.

    I just put a hydro flow control on the front port of an air cyl, and then up to a larger pipe/resevoir that would hold 2x what the cyl would, and then it was all air beyond that point. Fill the front half with fluid and down the road you go. Works great!

    I guess I never tried it, and maybe Adama is right, but I'd at least try shutting the regulator down to 150/200 and give it a shot on reg hydro products. I have one bank of machines that actually runs at 400psi. Also - when we shut down the pressure on our lathe chucks, sometimes we get down in the 250psi range I think.


    ----------------------------

    Think Snow Eh!
    Ox
    I do NOT know it it fits the OP's needs at all, but... traditionally, when we want fine-grain control, we don't so much look to lower-pressures. We look to uber-fine-grain differential balances between opposing medium or high pressures.

    Power-steering to aircraft control surfaces to backhoes - that assures enough 'ergs' are there that the latencies of frictions and flow, plus the inertia of mass of the mechanisms and the external forces applied to them can be handled consistently and well.

    Parts-bin components, wide choice of them. JFDI.

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    Quote Originally Posted by Ox View Post
    I guess I never tried it, and maybe Adama is right, but I'd at least try shutting the regulator down to 150/200 and give it a shot on reg hydro products. I have one bank of machines that actually runs at 400psi. Also - when we shut down the pressure on our lathe chucks, sometimes we get down in the 250psi range I think.


    ----------------------------

    Think Snow Eh!
    Ox
    One of the ones i was involved with used a pressure regulator to drive a hydraulic motor to drive a rack - pinion arrangement, problem was we only wanted a 20-30Kg of push, face of it it seamed a easy job, reality was a fucking nightmare to pull it off. We ended up having to run the motor at high pressure but then run a high pressure regulator to restrict the output of the motor to hence limit the force. Problem was we also needed full retract force and whilst it ended up working with check valves, it was nothing like the simple thing you would thing it should have been.

    As to using stuff like glycerine as your working fluid, yeah great, problem is as its moisture level changes so does its viscosity + same for temp, it gets too thick when cold, same goes for using low pressures stuff or pneumatics, its all great in theory, but can be a reliability to maintain down the line. As to comparing it to biological processes, great but again the reality of doing it with mechanics is a whole different ball game. If it was easy no one would bother with biological heart transplants would they?

    Key thing to remember with nearly all automation, the idea is reliability, simplicity and fix ability. Automation is no good if its breaking down or a bitch to setup - run. its gotta simplify the task save time and be reliable or you end up in effect just employing a warm body yet again.

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    water works just fine.It has been used as a"hydraulic fluid"
    for years.Old mechanical pulp machines used large water driven cylinders
    to force wood against a grind stone.This was invented in something like
    18 dickity two.Select the right seal material and forget about it.

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    bill invented it?

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    Relays, plcs, you have electricity use an electric drive, way better control over a huge dynamic range.

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    Without knowing the actual requirements of what you are trying to do. nor what your budget is, for all I know you have a problem that can be solved with a $2 fishtank pump from eBay. (Seriously after getting tired of replacing the weird jabsco star shaped rubber pump pieces on my bandsaw I one day found out that the $2 fishtank pump on ebay has been the most reliable oil pump I have ever had on the machine!). Assuming this is an industrial type budget/system Sun hydraulics has one of the best line up of cartridge mounted hydraulic valves in all sorts of shapes and sizes, you can manifold them or buy the blocks and use them stand alone and they will do almost anything you need. We use them to help with all sorts of flow/pressure control at the high and low ends where I work. As far as low pressure I don't see the issue just turn the system relief valve down as low as you want to go and now you are at low pressure. What is the big deal?

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    What Ox alluded to is called air over oil hydraulics.Doesn't work for continuous flow in one direction but works really well in an oscillating circuit.
    Our printing presses use it to move and load the closed chamber doctor blade chambers in and out.Some truck braking systems use a variation also.

    What I like about hydraulics is the control,hate the leaks.Air on the other hand not to messy on the leaks but sucks on fine control.

    Our cutters use air to raise and lower the window guards.when everything is new,no leaks it has very good control.One small leak internally or externally and it goes to hell.

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    Just a thought, I work in a pharma plant and I noticed some of the tablet presses use lube pumps that are little gear pumps. Maybe look at some of the automated lubrication systems and see if any of this could be adapted?


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