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

[karl lambrechts]

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

 

[LittleInch]

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.

 

[karl lambrechts]

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?

 

[karl lambrechts]

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.

 

[BrianPetersen]

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.

 

[LittleInch]

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.

 

[TugboatEng]

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.

 

[73lafuite]

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.

 

[karl lambrechts]

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

 

[BrianPetersen]

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!

 

[73lafuite]

Hello,
I will help you anyway.
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

 

[karl lambrechts]

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.

 

[karl lambrechts]

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."...

Thanks in advance.

 

[73lafuite]

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.

 

[IRstuff]

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 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[karl lambrechts]

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.

 

[73lafuite]

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

 

[IRstuff]

Have you googled?

https://www.industrialjewels.com/micron-orifice/

https://lenoxlaser.com/shop/flow-orifices/tubing/ss-14-tubing/

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[karl lambrechts]

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.

 

[IRstuff]

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 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[karl lambrechts]

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 :-D