FLOW RATES - LITRES PER MINUTE VS PRESSURE. NON-LINEAR!

FLOW RATES - LITRES PER MINUTE VS PRESSURE. NON-LINEAR!

When salary earners have no pride or interest in what they are selling then they are merely salary receivers. It is disappointing to see how poorly equipped some sales people are.  For example, I needed some PTFE tape to seal up a pipe thread.  The salesman at the local hardware store took on a distinctly blank look when I asked where they kept the PTFE tape? ' No we don't have that.' he mumbled.  Dragging him around to the plumbing section I pointed it out to him. Never heard of it and couldn't care less if he lost a sale. Conclusion! The employer merely needs a body to stand behind the counter at minimum cost.

A young farmer informs me that a spray-gun he'd purchased from an ag supplier has a nozzle-tip with a two millimetre hole which according to the salesman 'means 2 litres per minute.' The worst is that he accepted this statement without question. Where do they dig up this drivel?

This got me thinking about the relationship between flow rates and pressure. IF A NOZZLE-TIP DELIVERS 1 LITRE PER MINUTE AT 1 BAR PRESSURE WILL IT DELIVER 2 LITRES PER MINUTE AT 2 BAR? The simple fact is this. For a nozzle to double its output the pressure has to be increased fourfold.

Here's how to do the calculation. You need to know the flow rate for a nozzle-tip at a specific pressure. Call this l/min₁ and the pressure bar₁

Example: Nozzle-tip delivers 1.8 l/min (l/min₁) at 4 bar (bar₁). What will the flow rate be at 16 bar (bar₂) or 4 times the pressure?

l/min₂ @ 16 bar = 1.8 x √ bar₂ ÷ √ bar₁ = 1.8 x √ 16 ÷ √ 4 = 1.8 x 4 ÷ 2 = 3.6 l/min

Where √ = square root

Check out the AITX 8004 VK Conejet on page 38 of the 51 M catalogue.

Here's the formula again : l₂ = l₁ x √ b₂ ÷ √ b₁

In the real world the flow rate or the pressure may not be specified.

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