Capillary Tube Liquid Flow - Pressure Drop

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Diesel injectors operate under 50+ pounds of pressure.

No capillary action here to explain.

What makes you think the pressure drop is very high? The pressure in the pipe may be very high, because the pressure is needed to work the injector, but that's not a pressure drop (BTW I'd have guessed more like 200 bar = 3000 psi than 50+ psi as Lyn says in #2, buy I haven't checked, he may be right).

If there is a high pressure drop it's for the usual reason - the flow is high for the pipe dia and length, giving high velocity hence high friction loss.

It may be higher. 50 PSI is where petrol engines operate.

Yes, I thought maybe you were thinking of petrols

• 5psig is very high for a manhole cover. Especially if it is moving towards an individual.
• 3psig will knock a brick wall over. That's bad news for the person standing downwind of it.

The forum could do with some idea of the value of <...very high...>.

Why, that takes the fun out.

I rather do a WAG. _{^{(Wild ass guess)}}

Try blowing a mouthful of water out through a 3/4" (19mm) hose. Easy and fast.
Try it through a 1/4" (~6mm) soda straw. Not so easy and fast.
Imagine it through a 0.5mm i.d. capillary tube. Much harder and slower.

Why was this not intuitive in the first place?

The reverse also can be experienced that:

Sucking through mouth like a straw pipe for cool drink with 19 MM dia will be very hard and difficult. But with smaller dia, say 6 MM SIZE,the sucking will be easier. With 0.5 MM will be easier to suck, but very less fluid alone will come to the mouth.

RAJESWARI.D