Fluid dynamics 2

[Biltwell]

Good day, I am new here and also not much a hydraulic expert but I have recently designed a valve body to be used on a horizontal band saw, This valve replaces a singular needle valve attached directly to the cylinder and now mounted about 36" from the cylinder. In the valve body is a needle cartridge valve with a toggle cartridge valve. The idea is to be able to adjust flow rate while also being able to lock the system completely. And it does work (sorta). When the valve is barely cracked open I seem to be having a flow issue. The fluid will flow for a couple of seconds then slow way down. And Ill have to keep opening the valve more and more until the flow rate is too high and that at that point it'll have consistent flow. I stuck to the same principles as the OEM valve and port sizes, IE 1/8 npt and 1/8 ID line. I've tried using 0w20 oil and that doesn't seem to increase flow rate at all. I could really use some advice/input on this one from someone with more experience than myself. Thank you!

 

[3DDave]

Time for before and after - put the original valve back and see if it still behaves the same as you expect. Can the push adapters be moved from your valve block to the original valve to use the new tubing at the new location and/or put it in series with the block and cap the new valve location or just open the new valve full bore and use it as a cap.

Also, what is the original part number?

 

[Biltwell]

3DDave, I can do that. I've gotta go out into the field this morning so ill give it a shot this afternoon when I'm back in the shop. Original part number is Parker N200B 2000 psi/138 bar

 

[Biltwell]

I did discover there is significant expansion happening with the oil lines. Ive ordered more rigid tubing. Ill be trying that out too.

 

[hydtools]

I'm going to suggest that the cartridge needle valve may be the problem. The original needle valve is rated as a 3-gpm valve. The cartridge needle valve is a rated 10-gpm valve. The difference I. The relative opening may be creating a different delta P at a given low flow rate making very low flow control difficult. Testing with the original needle valve makes sense.
Install the original needle valve either before or after the on-off, open the cartridge valve fully to provide no restriction and test the effect.

Ted

 

[Biltwell]

I did replace the lines with more rigid lines and it has solved the issue. I appreciate everyone's time and advice, it was good looking out! Thanks again

 

[hydtools]

Interesting.

Ted

 

[LittleInch]

One thing I missed before was that your flow path is the wrong way round. Normally you flow into a needle type valve from the bottom up.

Did you connect the new pipes the same way around??

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[hydtools]

That needle valve is bi-directional.

Ted

 

[LittleInch]

hydtools - agree it SHOULD be, but is surely better to flow from under to out. the sectional drawing is not wonderful, but is good practice normally to go that way?

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

 

[Biltwell]

LittleInch. originally that's how I did have it hooked up but reversed the lines when trying to diagnose this issue. Either direction didn't have any effect on the issue. I'm still not totally thrilled with the performance. So I am waiting on a new valve to come in. A 'true' needle valve with fine adjustment. The reason, I cant just go all willy nilly with trying different valves is, the cavity sizes which I'm sure you're all aware of is particular to the cartridge valves. And I'm limited on valve specs per the size of cavity I have and after testing these with zero issues for months, I manufactured 60 of these units and sold them. Then this issue presented itself in my unit that I keep at the shop. So far no one has reported any issues with their units but If they do I need to find a fix that wouldn't require me to remanufacture 60 units I've sense pulled them off my store and wont sell anymore until I can figure out this issue. I found Tognella might make what I need, It should be here in a couple of days, Had to order it from the Netherlands...

 

[hydtools]

LittleInch, 'surely better'? Not according to various cartridge valve manufacturers. Design for bi-direction. An annular orifice would be flow direction insensitive. I suppose you could make an argument for convergent flow versus divergent flow through the orifice created.

Ted

 

[LittleInch]

OK, fair enough. I was only thinking that there might be some play in the mechanism.



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