Orifice v Reduced Pipe ID to control flow rate

[MacomMech]

Looking for a bit of advice, and confirmation that I am on the right path.
I need to take a feed off oil system running at 10 bar, which will pass oil through a couple of devices before being returned to the sump above the oil line. Flow in the branch line to be between 2 and 4 l/min.

I started off looking at an orifice using:-
Q=C*A*sqrt(2*(P1-P2)/p)
Where C = Orifice flow coefficient (used 0.7 as a value), A = cross sectional area of the orifice, P1 = upstream pressure, P2 = downstream pressure, and p = density
ref: Wikipedia

http://www.en.wikipedia.org/wiki/Orifice_plate

This gives me an orifice diameter of 1.6mm for a 3.84 l/min flow rate. The orifice is a bit on the small side and may become blocked, if a make the orifice for example 3mm diameter then the flow rate becomes too big.

Pressure after the orifice will be atmospheric pressure (P1 - P2 = 9 bar) if orifice is at the end of the branch, the oil is returned above the oil line, and the gearbox is vented?

If I increased the ID to 3mm but increased the length to give me the 9 bar pressure drop, would I get the flow I'm looking for?

 

[MikeHalloran]

One advantage of an orifice over a capillary is that you can easily make the orifice removable for cleaning or for replacement or modification to adjust the flow rate.

Yes, you could use a larger capillary to get the same pressure drop and flow rate, but as you increase the diameter, the capillary gets longer pretty fast.



Mike Halloran
Pembroke Pines, FL, USA

 

[MacomMech]

Mike,

So I see, just done some calcs for 3mm and 2mm tube at different oil viscosities.

Any thoughts on multiple orifices in sequence?

I did calculations using the equation in my first post where the downstream pressure of orifice 1 is the upstream pressure of orifice 2 etc. Three orifices at 2mm diameter would get me from 10 bar down to 1, with a flow rate of 3.47 l/min.

Am I missing something?

Matt

 

[cvg]

how about an orifice and a throttling valve in combination. just close the valve until you get the desired flow rate...

 

[btrueblood]

The Lee company has done a lot of the math on multiple-orifice fluid restrictors, you can learn quite a bit by getting a copy of their technical manual/catalog, or perusing their online literature.

http://www.theleeco.com/LEEWEB2.NSF/AeroStart!OpenPage

http://www.theleeco.com/LEEWEB2.NSF/Engineering!OpenView

I've attempted to produce, in a former life, a similar product to their viscojet...we came close, and spent quite a bit of money and time to get there. I don't much care for their service nor price when volumes are <10,000 units, but they do produce good parts.

 

[MacomMech]

A valve would be too easy! I want to keep away from valves, it is something that can be changed after the system has been set up, and the oil, hopefully, has lots of tiny bits of wear debris which can get stuck in valves.

I'll have a look at the Lee company literature.

 

[MattNCSU03]

You might look into a plug reistant orifice as well, I have used seen guys (

http://www.cuservices.net)

in power plant applications, they may have something that works for you. (They were also the first hit when I did a google search for "plug reistant orifice oil")