pressure requirement to give correct flow through orifice

[jouleflow]

Hi,

this is my first post please bear with me if it has been asked before.

Is there a formula that will give me a reasonable estimate for:

What pressure is required to send 60 litres / min of standard hydraulic oil through a 1/4" diameter orifice?

Thanks

Greg.

 

[3DDave]

https://en.wikipedia.org/wiki/Orifice_plate

 

[jouleflow]

Thanks 3DDave

the link is great but the maths are beyond me.

Would it make a difference if I said the pipe bore was 1/4" diameter @ 100mm long instead of an orifice?

 

[LittleInch]

RO calculations are a bit shrouded in mystery for liquids especially.

I found a couple of on line calculations and the answer seems to be around 17 to 20 bar differential, but as the velocity goes up the change in flow per differential pressure seems to go down.

you're looking at about 35 m/sec through your RO which is getting pretty serious and maybe you're getting into choked flow / cavitation issues at that rate which causes all sorts of problems.

I haven't got the paramters for oil exactly, but you really need to find an RO vendor and get them to give you the data.



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[jouleflow]

Thanks LittleInch

thanks for your reply. You have confirmed half of my calcs with the flow you quoted. Luckily the flow is 60 l/min or 1 l/sec this easily equates to a flow through a 1 cm sq area as 10 m/s or 36 km/h. With a 1/4" dia aperture being approx 33 mm sq it increases the flow by 100/33 x 10 m/s = 30 m/s roughly speaking. I see in the installation, part of the circuit looks to be about 5mm diameter so the flow at this point is 20mm sq area 100/20 = 5 so 5 x 10 m/sec = 50m/sec or 50x3.6 = 180 km/h which seems very fast to me. I assume a huge pressure is required to just get the oil through without the work required at the actuator. Incidentally all we need is for the 80mm diameter actuator to move 200mm in 1 second with 5 tonnes of force. It just looks to me that there is far more energy required to force the oil through the smallest part of the circuit than what is required to perform the work. I have also assumed that the smallest restriction determines the pressure required to give the required flow assuming no work is required & no friction.

I just need to confirm to the client that the restrictions are having a huge effect on the power consumption & that there may also be cavitation issues, also I want them to appreciate the huge flow speeds at certain points which may get very hot. Are any of the flow figures above unrealistic or outside general best practice?

Thanks again

Greg.

 

[LittleInch]

Hydraulic systems operate differently to transport systems which I'm more used to, but if this orifice isn't there for a reason (i.e. to restrict flow or reduce pressure), then velocities of that nature just eat pressure or reduce flow.

Any long term operation would probably result in some sort of erosional issues.

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

 

[jouleflow]

Thanks LittleInch

I now have enough info to present to my client.

regards

Greg