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# How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?2

## How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

(OP)
In a lab system, the pressure in the accumulator (500 ml) has to be relieved (automatically) in 24-72 hours.
Pressure at the input is nom. 380 bar (and has to drop to 0 bar). The output side is an open container (ie with a lid and diaphragm), so at 0 bar. The high pressure is used for an hydraulic braking system. The aim is to go for a passive system, so without controller or electric valve, and the idea is to put a (very) low flow control valve parallel to the braking system. This principle will result in a small continuous, but acceptable, leak during operation, because that will be easily compensated by the hydraulic pump (ca 1L/min), and this loss is negligible in comparison with the consumption of the brake system. We tried using an ordinary flow control valve, but due to small impurities in the fluid, the valve gets clogged sometimes, witch is unacceptable. A valve which opens wider when pressure drops, would give a more reliable operation.( Even 144 hrs is acceptable).
Open to ideas.:-)

At the end it will have to be integrated in a hydraulic block with 2 input ports and 2 outputs.
It would be very nice if we could find this somewhere as a standard part (total quantity is ca 150 pieces)

Thanks

Karl
AKLA

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

Does the flow need to be constant? You could use a solenoid valve with a wider opening and pulse it to give an average flow of 1 LPD. Increase the pulse duration as pressure drops for more constant flow.

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

Orifice with a filter cage in front?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

Hello,
The smallest pressure compensated fixed flow regulator Pmax 500bar that we find go down to 0.045l / min.
In very small flow rates like this, we see that it is not impurities which block the passage of the fluid but large molecules (polymetacrylate additive type) which block the clearance especially when the pressure drops.
cordially

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

(OP)
73lafuite: when you say "very small rates like this", do you mean the rate i'm asking, or the 45ml/min you mentioned?

Tugboat; no, the flow does not need to be constant, but i'm looking for a passive system, so without electrical controlled valve. But it is still an escape route.
Littleinch: I first considered, but it would ask for maintenance, and seen the answer of 73lafuite, it would be very close to impossible.

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

What maintains the pressure in the accumulator?

Can't you just relieve this pressure instead if it's a gas?

You don't actually say what the flow is that you want. That would help.

But if you're talking flowrates where you're worried about large molecules then I think a re design is required.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

(OP)
Hi LittleInch
By a pump 1 liter/min,
Relieving the gas is not possible because it is an diaphragm accumulator 300 ml (completely closed, no afterfill possible).
Flowrate is as in title 500lm/24hr up to 500ml/144 hr, that is 0,045 l/hr or 0,0007 l/min. Less would be also ok

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

Why why why why why?

Why do you need to do this?

If this is for an "emergency braking system", what's wrong with it holding pressure indefinitely?

If the pressure has to be released after X time for who knows what reason (and WHAT IS that reason/excuse), what's wrong with just dumping pressure at that time all at once?

What's the reason for dumping pressure in your "emergency braking system" accumulator at all?

If it's to remove a stored-pressure hazard for someone working on it, do you really want them to wait three days for it to bleed off pressure? Give the maintenance chap a pressure-release valve and let him dump the pressure at once, the moment he has to work on it!

You are never going to fulfill your requirements "as asked". So go back and ask why the system is being specified in this manner.

The last vehicle I had which developed a leaky master cylinder (due to it being almost 30 years old) ... got a new master cylinder so that it didn't do that any more.

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

(OP)
It is not an emergency braking system, it is a security for a lab braking system (for the moment).

Point is that it must be a passive and automatic system, so that is without electrical valve and without manual push button. In this case the system will be safe after a few days: even without electricity and without human intervention.
The spec is made with care, there is no reason to question the spec, the aim is to solve the spec.

Don't only think car : that is merely 1 of the 1000's of applications with hydraulics.

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

What are you "braking"?

Is retained pressure causing the brake to "apply", or to "release"?

Why is it a good thing for this to apply or release after two or three days and not immediately and as opposed to being able to release upon demand - and if this achieves the "safe" condition then why is it okay for it to be "unsafe" in the interim two or three days?

I still maintain that what you have described so far is not practical to achieve in the real world, which means you need to go back to whoever wrote that specification and find out (A) what they really mean, (B) how others have achieved compliance in the past, (C) what the fundamental underlying requirements are.

Ask WHY. There's a reason I asked "why" five times. Frequently that is about the right number of times it takes to ask "why" in succession, to actually arrive at the underlying reason why a certain thing happened a certain way.

I explained my example. It's a car. You explain your example. The rest of us have no clue. We can't read your mind.

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

So, you're basically asking for a passive leak, which could be done with a small orifice; for a flow rate of 12E-6 scfm https://lenoxlaser.com/resources/calculators/orifi... says about 2 microns at the initial pressure. Their equations are here: https://lenoxlaser.com/publications/fluid-flow-thr...

Since the flow rate is dependent on pressure, you'll need to iterate the equations

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

Hello,
Strongly agree with BrianPeterson.

You can always go on saying that your specification is made with care, and that you should not question it.

However, your leakage rate is "unachievable". To explain it I would have to explain to you the phenomena of drawer sticking, filterability, and leakage which decreases over time in an electro-distributor whose drawer does not move relative to the body. I have 45 years of experience in the safety brakes and we delivered equipment that maintains the pressure for months without the pump ever recharging the accumulator. Reminder: a drop of oil is 0.06cm3 and you want 7 to 2.3 drops per hour !!!!

Please tell us when you have the solution.

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

(OP)
Dear gentlemen,
It is in a lab environment. It is a brake system, more important it is a hydraulic circuit, in which a passive relieve (safety) system needs to be build in. The hydraulics are small (in the world of hydraulics). This setup was to test electric motors, but it will eventually used in all our systems.

Why, why, why, why, why...???

Lab systems are used, but suddenly are moved to a storage room ("project is in frige") where they sit for months,years,... Then another person, student, newbee, cleaning personnel, project manager, engineer, (in this case a person with many -25..26?- years in the company)... takes it up, not knowing that there is still high pressure in the system... Time, oil, made stickers fade and fall of... Deterioration, corrosion did the rest... There are regulations ("do not store under pressure", "check pressure first", "2e person check",...) everywhere, but we are humans, so mistakes are made. On the door, the same "DANGER" symbols, and still...
There is never enough attention for danger: Planes crash, rockets explode, everyday there are accidents everywhere, on the job, on the way to,...

So passive safety must be integrated! So a technical solution to relieve pressure, without action, without electricity is a must. "Unachievable" things do only exist in the mind of people who cannot find a solution. Going to Mars was once unachievable, and going to the moon is still never done, according certain persons.

Therefor that specification.

We did the brainstorm sessions (engineers, managers, safety/quality personnel...) and this is what we came up with. If you have another solution, or if you have a complete other approach to solve this, or if you see a way to change the specification, we will be very happy to hear about.

Thanks

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

You seem to have manoeuvred yourself into a position where loss of pressure is unsafe and unacceptable - but so is not losing pressure - and are now trying to negotiate a way between these two incompatible requirements by exploiting a difference in timescale between the two types of hazard. That prompts a few questions:

I don't know the detail of your testing process, but it sounds a bit like you are converting your braking system into one where the brakes release themselves without warning after a few hours. Are you absolutely certain that, when this happens, it can never lead to danger? Every year, I hear at least one new story of some unfortunate individual chasing an artic across the yard, or a locomotive down the hill, after they've started the engine without checking the parking brake is set, then gone off to have a brew while the cab is warming up and the brake reservoirs are charging.

You mention a window of 24-72 (or maybe 144) Hr for discharge of the accumulator. What governs the 24 Hr end of that window? Even allowing for a nonlinear pressure decay and the brake needing a respectable pressure to work with, that feels like a very long time to have to keep pressure available after the pump has died. Is it possible to adjust the process to put it into a safe state much sooner - which would allow you to depressurise the accumulator more quickly?

Is it possible to do a more fundamental redesign so that the brake is held off by the hydraulics working against a spring, and applied by spring force? This would give you a passive solution to the braking requirement allowing you to reduce the stored energy in your hydraulic system (note, though, the potential for becoming another unfortunate individual when you restart your brake pump).

A.

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

There is another parameter you can tinker with:

Simply make the accumulator much bigger. Once it's larger than 65 litres, 73lafuite's valve will sort you out very nicely indeed. (Please don't try doing this).

When an idea as bad as that is the most obvious fix, it's a strong hint that you've set off down the wrong path.

A.

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

No one is questioning the need to relieve the pressure. I, at least, don't understand why it is required for device to remain in an unsafe condition for several days. Let it leak down over an hour. Or 10 minutes.

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

I deal with risk management in industrial environments all the time.

Stored fluid pressure is indeed a line item on the risk assessment.

One of the things you absolutely must come to terms with, is that risk can not absolutely be eliminated. You just can't. At a certain point you have to rely upon someone to actually apply the padlock to the electrical disconnect before going inside the machine - and trust that the electrical disconnect is correctly marked, shuts off the correct equipment, etc. YES people fail to lock equipment out, it happens all the time. And then you have to rely upon someone to not flip the "on" switch and press the "start" button when there is someone inside the machine. YES this strategy can fail, and it does fail from time to time. But you just cannot completely eliminate the risk.

You can "reduce" the risk.

If you're worried about the equipment being stored with pressure inside it, give people a valve that they can easily open to release that pressure and instructions on how to use it. If you're worried about someone opening a fitting on a pressurised hose because they forgot to properly release the pressure, use a threaded fitting that will start to leak slowly the moment someone puts a wrench to it before it goes kaboom. If you're worried about a printed sign fading or disappearing, engrave it (or the most important bits) on the tank itself. If you're worried about it rusting, make the tank (or specifically the engraving) out of something corrosion-resistant. If you're worried about someone not being able to read English, use the appropriate ISO warning symbols. If you're worried about someone not understanding those signs ... you can't fix stupid.

Hand in hand with any CE-marked piece of equipment, is the instruction manual - "information for use". How to install and connect the machine. How to stop the machine. How to prepare the machine for storage. How to prepare the machine for servicing. What procedures to follow when doing so. And, information on risks associated with all of these procedures, and how to mitigate those risks. Invariably, people will be called upon to follow the correct procedures for doing things in order to avoid causing a problem. It's unavoidable.

Your responsibility as an equipment manufacturer/integrator is to prepare that information for use.

Your responsibility as a user is to follow that information for use. And keep that instruction manual so that people have access to it. And provide relevant people with training for that equipment.

Once again - you can't fix stupid. But sometimes you can organise it so that they just get soaked with sprayed hydraulic fluid instead of being exploded.

And yes, we've had that happen ...

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

And one other thing. Any pressure vessel ought to have a readily-visible pressure gauge.

Yes, a pressure gauge can fail, too. But if something is stored with (let's say) 100 bar pressure inside it, and then is left to sit for years, the most likely outcome is that the gauge would seize with the needle showing 100 bar even if the accumulator loses pressure over the years. A pressure gauge with its needle at 100 bar would give me pause before fiddling with whatever the mechanism is.

If someone chooses to ignore that ... you can't fix stupid.

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

(OP)
Hi 3D Dave,
Yes that was a consideration. In this setup a larger leak is not a problem, but we also have smaller systems ( we are a R&D company, prototype builder) , where the "leak" would influence operation. We want to do this development only once, we try to go for 1 standard solution in all our experimental set ups. Several different solutions can lead again to wrong choices. We consider 300ml in 24 hr can serve as a general solution. We never use accumulators larger than 1L.

(Some systems do require a pressurized system all the time :for example emergency brakes needs to ne ready all the time.)

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

(OP)
Zeusfaber,
No, we are looking for a device that reliefs the pressure very slow. It is a lab test system, so it operates under supervision, and only short. This time it is a motor test system (with brake), but this is not relevant. We are looking for a standard passive system, that relief the pressure slowly.So, after x hrs or x days, any prototype system is safe, even for people who does not know anything about pressure and hydraulics.

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

I have finally understood what you're trying to do, which is generally a good thing, but your volumes are so low that it becomes unfeasible.

I think you need to look at battery powered things, which fail safe, so if the battery runs out then it doesn't work until you replace the battery. Or you plug in a low voltage power supply with a rechargeable battery. That's detail.

Then you could instigate a simple push button timer which counts down the hours left pressurised, where a press of the button resets it to say 72 hours so it won't power down over the weekend, then at zero it opens up a spring loaded held closed solenoid valve and dumps pressure in say 30 seconds via an orifice.

You need to see the practicality here, i's 1/2 litre of fluid here, basically a can of beer, and you're trying to drip the contents out in 2-3 days. That's just too small a flow to do reliably. IMHO.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

(OP)
Hi Brian,
Whatever you do, when there is a instruction that says to do something manually, sooner or later somebody will forget, it is just a matter of time. ( And that doe not mean the person is lazy, or careless, it is a human, and he can have a bad day, and humans just forget)
In a production area, on a finalized machine, you can create safety measures and give trainings to people. But in an R&D section, projects evolve, people change, and sometimes there is time pressure. A very bad combination.

There for the aim is to build in , as a first step, and as a standard part, a pressure relieve device.

So, now you know almost everything, do you see a solution?

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

(OP)
Hi LittleInch,

The scope is to find a passive solution, so without batteries or electronics (batteries die or need to be recharged, electronics fail or can be passed - we do not want to introduce parts which require maintenance or special care because that are reasons to leave them out). If that seems impossible - hard to believe- we will go back for a solution with electric power. (Indeed a timer which get a reset when the pump starts and closes the N.O. pressure relieve valve.

Such a low flow will be for sure not be stable, but only zero flow (blocked flow) is not allowed. 24 hrs-72 hours is asked, but if it is sometimes 12 hrs and sometimes 144 hours, everybody will be very happy.

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

No. The controlled-leak that you want to achieve is too small to be reliably achieved without being zero.

A normally-open pneumatic/hydraulic directional valve, electrically actuated to close it but spring-loaded to the open position, can be used to dump the pressure the moment someone turns off the power to the machine. Just dump pressure straight away when (A) someone unplugs it, (2) someone switches off the main disconnect, (3) the lights in the plant go out, etc. That's easy and if you want to not have stored pressure in the machine, that's the way I'd do it - in conjunction with a pressure gauge on the tank. No pushbuttons, no controls, no nothing. Forget about trying to do it over a couple of days.

If the valve seizes in the open position (most likely event, in the case of long term improper storage), the machine won't work because it can't build pressure.

If the machine is only used (power-on) for short periods, it is exceptionally unlikely that this valve would seize in the closed position, but you have the pressure gauge as a back-up to tip off the operator if this happens.

It is possible to buy such valves with spool-position monitoring and internal redundancy so that automatic control systems (which need a certain level of sophistication, but it's not rocket science) can prevent the machine from starting if it is in an unsafe state (e.g. automatic depressurising valve spool seized closed).

We do this all the time, for production equipment. But ... the 110 ton stamping press that I need to go look at shortly to investigate a re-tooling, is what I would consider to be a small machine.

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

Brian - Best plan yet.

If your vessel is 500ml and your pump does 1000ml/ minute then you only have to wait 30 seconds if you do it accidentally.

Simple, neat, fail safe.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

Having a system that slowly becomes safe over a long period of time isn't safe as it won't be clear exactly when the system becomes safe.

There are valves that will stay closed when pressure from a pump is applied and will open when pressure is removed. This seems like it would be a better solution to your problem.

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

Hello sir
The hydraulic accumulator with gas is not a new technology. It was Jean Mercier, a Frenchman, who created the Olaer company in the 1950s and joined forces with Monsieur Green to distribute this product throughout the world. And since then there are simple regulations and techniques that ensure safety.
It seems that you have studied and are able to explain a lot to us. Congratulations. On the other hand, you must really lack experience in your company. Your system is however super simple and there are thousands of applications with accumulators and solutions that easily meet the regulations. Look at what is being done and find out from your suppliers.
For my part, I no longer want to help you since you are constantly closing the door to get us your science.
Cordially.

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

(OP)
Hi Brian,

Ok, thanks, that is an escape route... Only problem is that in some (simple hydraulic) systems we will have to introduce electricity to function now, just to close a valve... Stuff to discuss, i'm quite sure...

One thing was intriguing: you said that molecules block very narrow orifices or valves. Large C-molecules in oil have dimensions max ca 10's of nanometers, so I guess that other things come into play to clog things - molecules sticking together?. But short, how small can an orifice be, without being afraid it will be blocked one day, because of this phenomena?

(A last shot may be to put several (and more than several such orifices in series... Also the idea of a very long and very thin pipeline came up...(however viscosity will have a larger influence in this last case).

To be continued

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

If a molecule doesn't block it, a piece of dust will. Can you reliably assure such total fluid cleanliness?

If someone can't be trusted to follow a lock-out (including depressurization) procedure, which is something they are legally obligated to do, can they be trusted to replace filters, wear hairnets, follow clean room procedures, etc.?

You are barking up the wrong tree!

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

Hello,
With the best of check valves when it closes by pressure, we see that we have a leak which slowly decreases to become zero in 5 to 20s.

With a standard NG6 4/2 spring return spool solenoid valve, if it has been energized for hours, it may happen that when the coil is cut it takes several seconds for the spring to push the spool. I had the problem on a safety brake in Greece in the 80's with an Italian product.

At 10-20 bar on the P of a closed center NG6 spool valve, A and B closed, T at the tank: We can see that there is no longer a leak at the T after a few minutes. If the spoll is moved slightly with manual assistance, it leaks and then becomes waterproof again.

For me, it is the largest molecules in the oil that accumulate upstream. Even with super filtration we have the problem. And this stacking of molecules manages to block all passage. Even with super filtration we have the problem. With oils having good filterability, it clogs less.

Your idea of ​​putting sprinklers in series is a very good one.

Maybe you can take a look at Lee Compagny's. It's a serious old company and they can help and provide you with these sprinklers.

In order not to make a nozzle of very small diameter which risks clogging, several must be placed in series. A commonly used economical way of doing this is to take a headless screw or threaded rod and thread into the drilled block. In M4 or M5. With a triangular file or a machine tool make a groove parallel to the axis at 60 °. Then with a small diameter wire (taken from an electric cable and measured) and a nut you can control the passage section.

cordially

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

(OP)
Hi Brian,
Nobody can't be trusted to follow procedures: If everybody did what would be (legally) required, no accidents would happen. In fact, safety systems would be redundant... Thing is people will make mistakes, whatever you do. Make a bend in a road, install speed limits, flashing lights, warnings, alcohol controls, police, and still, sooner or later -no matter how hard you bark - a driver will miss it.

An automated system (well designed - and that we can control) is safer than humans.

btw We are overthinking our clogged flow control valve: We assume, thanks to your explanation, that the very small opening clogged due to molecules, and not due to impurities. Therefor the idea of larger orifices ( sprinklers ref Lafuite) in series came up.

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

(OP)
Hi Lafuite,

Sorry, I (we ) do not understand "With a triangular file or a machine tool make a groove parallel to the axis at 60 °. Then with a small diameter wire (taken from an electric cable and measured) and a nut you can control the passage section." We would be really appreciate if you can explain so we understand.

But, we did a test: M9, thread 1 mm (fine metric), screwed in a block, for about 10mm. The opening, more or less a triangle/circle segment (between the top of the rod thread and the deepest point of the bold) would have about 0,02mm² . Just a figure because hardly to estimate due to tolerances. In fact we formed a spiral pipeline of about 30 cm.(+ presumably some parallel leaks)
300 ml starting at 380 bar, gave us ca 5 min... So when going to and M4, and longer ...?

So we are looking forward to your "... make a groove parallel to the axis at 60 °. Then with a small diameter wire (taken from an electric cable and measured) and a nut you can control the passage section."...

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

Hello,
A sketch of the machined groove. If there are 10 threads this makes 10 nozzles in series. We consider the zero flow in the helicoid of the thread.

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

If you're going with a leak, then you could use a manufactured orifice as I suggested earlier.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

(OP)
Hi Lafuite,

Thanks! Good approach, (new to us) however the idea needs further overthinking: in the test we did, only the flow in the helicoid of the M9 thread was already too high. Some rough calculations showed we need an orifice of 0,05 mm - 0,1 mm max, and a few tenth's in series... To prevent blockage, we prefer to go to a larger diameter, compensated by using more orifices (or longer pipe).

It may be a way to a solution, but we think we have to combine several approaches fe. a standard flow regulator + series of orifices + ? thin pipe. (A very long M6 hole -100mm- with thread all the way bumps into production issues.

We realize (that by going the passive way) we are probably still a long way from home...

Hi IRstuff,

Do you know a supplier of micro orifices? They don't need to be very accurate.

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

Hello,
One last idea. After I stop. My experience is more in the large powers in closed circuit or with logic valves.

On mobile machines there is also an assembly which prevents the nozzle from being blocked by particles. For example a ø1mm nozzle in which we thread a resistant steel wire of ø0.8 This wire is twisted on both sides of the nozzle so that it does not pass through the hole. Advantage: as the wire moves when there is no pressure, the particles loosen. You can perhaps pass the wire through nozzles in series.

Have you contacted Lee Compagny? They have been specialists for well 70 years in your field of research. I am sure they can find the solution for you. I don't know if we can still find a lot of details on the internet, at the time they had paper documents which had helped me a lot.
cordially

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

(OP)
Hi Guys,

Lafuite, great idea!! How it is possible that we (here in the company) did not find that idea anywhere on the internet, or that no supplier came up with that? Cleaning + smaller orifice, great start, thanks! (Little bit afraid of breaking and losing it into the hydraulics, so last orifice without cleaning, or a filter to add)

IRstuff, yes, we googled (far too much - but older guys know that it is far more efficient to ask the right a professional ). We found a few companies but too far away. Special things, design fase, small quantities, and plus being far away , perfect situation for being forgotten... So preferably closer to home ( Belgium). Thanks anyway!

Let you know.

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

OK,

I do have a silly story related to this. We once built a piece of equipment that needed to be sealed so we were concerned about overpressure during a diurnal cycle. Argued about bladders and relief valves for about 4 hrs during our concept review, but couldn't come to any conclusion. Months of anticipation was rewarded when we first purged the unit during initial integration. The overpressure lasted for about a minute; so much for a decent seal.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

### RE: How to realize an extreme low flow pressure compensated flow control valve 1L/24hr - 1L/72hr?

(OP)
IRstuff,

I recognise... discussions for hours, and at the end, there was absolutely no need to. Unfortunately, the opposite also happens. Everybody knows that little detail that just stayed under the radar of everybody, and caused so much trouble afterwards...

Talking about bladders... we have a next application. We are looking for a (preferably) diaphragm accumulator, without any permeation... . It is also a lifetime issue and we cannot dump the N2 somewhere. It would be used in a vacuum application (not extreme high vacuum) and outgassing must be avoided. Saying that the outgassing issues where solved was not good enough

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