Laminar Stream Bounce and the Low Pass Jitter Filter Problem

Hello All...

I'm having a problem similar to Werner_Tom where I have an issue with the Laminar stream breaking apart, but I believe mine is related to the low-pass jitter filter.

I have 15 inch (38cm) long long by 6 inch (15cm) wide laminar nozzle which uses a 1/2 inch (12mm) outlet. I have in place a low-pass jitter filter which is 2 feet (60cm) tall and has 3/4 inch (19mm) inlet and 3/4 inch (19mm) outlet. The inlet is controlled with a ball valve.

When I first turn on the pump and the stream starts to flow I get a very good laminar stream at both low pressure (short throw) and high pressure (long throw). But after about 30 seconds the stream begins to fluctuate and bounce around. It seems that it takes about that long for the low-pass filter to completely fill with water thus forcing the air pocket out of the tube and without the air pocket there is nothing to absorb the fluctuation in water pressure from the pump.

Does anyone have any idea what is going wrong with the low-pass fillter, why it is filling with water and how to eliminate the problem?

Here is some video of the stream...







In case anyone is interested, here are some pictures of the nozzle I have built. The idea I had for this nozzle was to construct a decent laminar flow nozzle using only parts that could be obtained from a home center (Lowes or Home Depot in my case), a garden center, Radio Shack and a couple of online parts stores and/or E-bay and with basic home-owner friendly DIY tools (a drill and a table or reciprocating saw). The thought was to design and build a nozzle for those of us that don't have access to a fully equipped machine shop and/or industrial manufacturing components. That is, for those of us who are "friend-in-the-business" impaired!

Anyway...the nozzle I built is constructed from 6 inch (15cm) PVC. It uses 2 types of foam filters. The first is a filter media I got from a garden/pond center that is used for filtering large particles from ornamental fish ponds in a bio-filter. The second type were kitchen scrub pads. I used about 1500 5 inch (12cm) stir type straws. The light tube is 3/4 inch (19mm) pvc pipe with a clear plastic pvc cap. The light kit was purchased on e-bay and consists of 75 individual fiber-optic strands and a light control box wich puts out a rotating pattern of colors. Only about half of the strands fit in the light tube, the rest will be used later for other fountain decorations. The outlet is a brass connector used for connecting PEX tubing.

Anyone would like more information on the dimensions and/or parts list for the nozzle, please let me know.

I couldn't see you pictures or video, but I read through it and IF you low pass filter is filling up, then that is the reason for your pump jitter.

The object of the low pass filter is to have it partially filled with water. As the water pulses from pump, the air gap will act like a spring and the pulses will be damped out.

If your filter is completely full of water then it is acting like the filter isn't even there, and the pulses are being transmitted to the nozzle KILLING your stream.

Make sure that your filter is completely air tight.

Thanks John.

When I built the low pass filter I used 3 inch PVC and drilled holes to insert 3/4 inch pvc to make my connections to the hoses.

I guess I didn't get the holes sealed up well enough with the silicone to prevent air leakage.

I bought some new parts last night which will allow me to construct a new low-pass filter using all fitted pvc parts, so no drilling and silicone will be necessary. I'm going to assemble it after work today and give it a try...hopefully I will get better results.

By the way, are you still not able to see the photos and videos that I had included?
If not, here is a link to the photobucket site if you want to take a look.

https://s862.photobucket.com/albums/ab187/dlkempf/

And the videos...

https://www.youtube.com/watch?v=LnHD6-970wY
https://www.youtube.com/watch?v=coDE-mI5YfA
https://www.youtube.com/watch?v=eo1Nk09uUNA

Thanks!

Daryl

I built my new low-pass jitter filter last night, and the new (air-tight) design is working great!

I now get a perfectly clear laminar stream throwing 6-7 feet long and about 3 1/2 feet high!

Any further than that I do get a bit of a break-up, but I think that may be a function of the size of my nozzle as it is only 6 inches.

Here are some pictures of the new filter. Once it stops raining I'll post some video of the stream.

What a great setup

I love how simple you made it, and it works

I have trouble with my new built laminar .. maybe I should try a low-pass filter...

Where did you get the brass fitting for the outlet? Did you make it or buy it?

I bought the brass ring for the outlet at Lowes. They cost about $0.82 each. It is actuallt a stock fitting for connecting PEX pipe.

As you can see in the picture it comes with a barb end on it for insertion into the PEX to accept a crimped fitting.

I used a dremel tool with a cut-off wheel attachment to cut the barbed connection off as flush as possible with the bottom of the fitting and then used a standard bench grinder to file off the remaining burrs and flatten the piece out. Once that barb is removed and flattened you are left with a piece of brass with a perfectly round 1/2 inch (12.5mm) hole with a very sharp edge on the bottom and a chamfered edge on the top. The piece also measures 1 3/8 inches on top and 1 1/8 inches on the bottom, so the small step allows for a ledge to be drilled in the material that holds the outlet nozzle (using 2 different size drill bits) so that there is a glueing surface and makes a very strong water-tight connection.

I tried to find these at Home Depot, but the ones in my area don't carry these types of fittings.

If you don't have a Lowes in your area and would like to try using some of these fittings, let me know and I would be glad to send some to you.

Thanks!

Daryl

Great, thanks for the info. I do have a Lowe's around here so I'll have to pick that up. BTW - what kind of pump are you using?

I use a Pond Master Mag pump which is rated at 1200 GPH (4500 lph). It has a 3/4 inch (19mm) inlet and outlet.

I got it (on sale) last year at Home Depot for around $120.00.

It's a great pump...very quiet and very efficient.

Right now, it's a bit more powerful than I need as I have to really throttle it down by restricting flow into the low-pass filter with a ball valve, but it will certainly come in handy later on when I want to add more features to the setup.

Daryl

Well the rain finally stopped here in Western New York long enough for me to get a bit of video of my laminar stream with the low-pass jitter filter in place...

Thats awesome. What is that green device banded to the outside of your nozzle?

Thanks!

The green device is my new thumper unit...check out the new thread I was just posting and let me know what you think.

https://laminar.forumotion.com/laminar-nozzle-talk-and-pictures-f1/rudimentary-thumper-unit-t64.htm

Thanks!

Daryl

WOW, Relly nice Job, congratulation, the Filter Works amazing Great! thanky for your videos!

Mario