IRNUKE has it right but you need more than 1 inch for the stream to recover on the low pressure side, I think you need roughly 3 inches after the outlet at a mimium. You can also have priming issues so you should test first to make sure its in the right place before you decide where to put it. Some pumps like to have the outlet closer.. some farther than the target of 3 inches. I had this issue recently and have not had a chance to work on it. Perhaps this weekend I can.
Bingo Bob hits the part that got left out. Its Tapered. The Taper is the important part. Look at the drawing earlier or the picture of tubing and show me the taper? rcengr is correct about using a converging/diverging nozzle, according to my research the angle on the converging part (Inlet side) is not super critical, but the outlet side needs to diverge at between 5-8 degrees so the flow doesn't separate from the wall of the nozzle. Going from a 1/8" radiused curve on both inlet and outlet side of the nozzle to a 1/4" OD 10 degree converging/diverging nozzle (made with a 5 degree tapered endmill) gave me a 28% boost in output from 2.1 to 2.7 gpm with a brushed motor. The percentage would be slightly different with brushless motors but I never tested that after I made the nozzle I use about 4 years ago.
Sometimes when I turn the pump on it will go into the tall stream. I just turn it off/on again and it goes back to the laminar flow.
That's where the angle of the exit taper is critical. My Vanguard had one outlet that was 100% on kicking off correctly and the other built using a different taper would perform like Bob mentioned. Just a quick flip to drop pressure and let the large tube fill as the thin jet collapses. I suspect that given the right taper, the overall tube length could be shorter.
You are seeing exactly what I saw in simulation years ago when I looked at that. I recall looking at 7 degree tapered outlets and decided that it was too much to grantee the jet actually spread well and pressure recovery happened. I also recall a significant influence on the smoothness of the outlet geometry on that angle, but I would have to see if I can find the old data files and check.
Fascinating discussion. Looks like the Glug Glug is based on a venturi flow meter and 6 degrees is the optimum diverging angle to avoid boundary layer separation (#6 on the following link). Boundary layers "Increasing the angle of the diffuser increases the probability of boundary layer separation. In a Venturi meter it has been found that an angle of about 6 provides the optimum balance between length of meter and danger of boundary layer separation which would cause unacceptable pressure energy losses."
<Does a little happy dance> Who says memory fades with age? Now if only I could remember the phone number of that girl from high school in 1982.....
I'm going to test just gluing a tube to the end. Been real busy this week. I will try a 2.5" piece. no fancy milling equipment at my place.
867-5309. Your welcome. Say "hi" to Jenny from me (yikes, how old do you have to be to get this reference?)
SO... the thing I was unclear on and never found a labeled drawing for when I was reading up on creating a diffuser nozzle was how exactly the taper angle was measured. Is the angle measured including both the sides of the nozzle or is it measured from one side of the nozzle to the centerline of the nozzle? It makes a difference when selecting a tapered endmill (which are not cheap, $40 to $70) because the angle on a tapered endmill is measured between the centerline and the cutting edge, which means a 5 degree endmill cuts either a 5 degree or a 10 degree tapered nozzle, depending on how the nozzle taper is measured. I will say that I do get some sporadic flow separation from the side of the nozzle with the nozzle I cut with a 5 degreee tapered endmill, so was considering trying a 3 degree endmill sometime in the future to see if that was the problem.
Centerline Also, I don't see why a section from a funnel or adhesive cartridge could not be adapted for the outlet.
A 10 degree (each side) taper works. They are about $20 from mcmaster-car. Low angle tapers result in a longer outlet assembly that are hard to make fit and they don't help your flow rate much. Make sure you are using a new 1/8" drill bit to machine the center hole, else it will be larger than 1/8"and people will be mad at you.
Great SteveT, thanks for the pictures. Indeed there are some references to using the caulking tube tip as a nozzle in some old 1980s hullbusters, but I think it was as the inlet side. They liked the solid stream back then. Any taper works, but there is obviously some optimum angle. I have made some outlets with a 15 degree taper on the out side that work fine, but have not tested them versus other lower taper outlets. My normal outlet is about 3 inches long, is mounted horizontally and has no land in the middle in between the conic sections, I just stopped when a 0.124 pin would pass and a .125 pin would not. New drill bit, old drill bit, they are all subject to flex and will drill a 3 lobed oversized hole in soft material. A 3 flute tapered endmill drills a squarish hole when it flexes. If you insist it must be a perfectly round orifice you need to press a bearing through a slightly undersized hole to set the ID. Which is way too much trouble and impractical for most people. Anyhow this is what I use to make an outlet.
I have one on the Nassau and it works very well, but I can't go 22 sec in a 100 ft. when it's on like before,,,,,,,,,,,,,,,, I'm so sad.
I use Enco for my machining supplies. Here's a 7 degree taper mill with a 1/8" end: Enco - Guaranteed Lowest Prices on Machinery, Tools and Shop Supplies They also have one with a 3/32" end. Get yourself an undersize 1/8" reamer at the same time to make a perfect hole: Enco - Guaranteed Lowest Prices on Machinery, Tools and Shop Supplies It's also a good place to get SS hardware and free shipping over $50 through the end of the month if you use FEBUPS code.
