Help building a PVC bypass valve for venturi pump

andyinnycApril 21, 2014

My posting in the tomato section received the suggestion that I post here.

I'm looking to build a water bypass valve from PVC and parts from HD/Lowes to use with my fertilizer my tomatoes and peppers, etc. (a mazzei-type venturi pump)

A bypass valve splits the hose water either fully or partially and then rejoins the streams (one of the sides has a ball or other type full/partial shutoff valve) - one of my splits will have a venturi fertilizer 'pump'. See the picture at the bottom for a 'basic' unit in which the venturi pump is locked down (ie not quite what I want).

So, anyone have a parts list and directions - visually it's easy to see, but the fittings, etc. are easy to get wrong. I don't know, for example, what the various connectors create as offsets for the lengths I'll need.

One side difficulty is that I want the venturi side to have a replaceable (varying) length tube with connectors on both ends since my sample ABS venturi pumps are different sizes. The venturi will connect to a fixed end (screw connectors) and then there will be a 'stub' with screw connectors on both ends - the stub will have replacement stubs such that the correct pair (pump/stub) will fit the opening.

I'm hoping to find PVC connectors that screw on - like a hose - rather than turning the ABS pump (which won't work since it needs to be connected to both ends. One section (the stub) will be removable since the various units are different sizes.

My googling didn't pick up any plans or diagrams - which seems really weird since this should be an afternoon project for anyone with a PVC cutter.


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Not sure if this helps or not, I also have a mixture meter not seen that is inline on the drop hose allows for fine adjustments. I used 3/4 PVC I can boost the amount of water through the injector this way by throttling the main and before and after the injector. The injectors are 10.00 on ebay!

As far as a parts list I took mine to lowes and assembled it in the pipe department.

    Bookmark   April 21, 2014 at 9:15PM
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The injectors are even cheaper than $10 on eBay.

My only concern is a response that the Mazzei 283 is MUCH smaller than the 1/2" ones I bought and works at much lower flow rates. I'm hoping that my test cases work for my drip lines.

Your bypass seems to have 3 valves - why?

Are there PVC to hose connectors that move in/out when tightened/loosened? I'm concerned about getting my unit in place to install/remove.

Since I'm going from hose to PVC to hose, is 1/2" or 3/4" PVC a better choice?

All the info I can get helps.


    Bookmark   April 21, 2014 at 11:36PM
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The 3 valves was per mazzei injectors I saw installed in green houses in our area. It allows us to throttle our injection down. I can shut the main line and run only through the injector but it slows the flow tremendously. With this set up I can partially close the main, run my mix heavier and adjust the flow with the other two valves. It also allows me to completely shut my injector off.

Our injector is semi permanent. If I take it out I have to cut pipe. It stays on that manifold.

I wish I would have gone 1 inch as that would match the rest of the pluming. We water over 2000 feet of grow bed. With this setup it takes around 2 hours to water every other day in the summer. What the injector is running we have someone near it that whole time so I would like bigger plumbing faster drip emitters as it would save me money and time.
The way I see your setup it is either completely on or partially on. I don't see a way to shut the injector completely off but I could be wrong.

    Bookmark   April 22, 2014 at 8:41AM
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Some reading for you. I can't find the information I got from Mazzie, but this has some info worth reading.

Here is a link that might be useful: Link

    Bookmark   April 22, 2014 at 8:45AM
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Thanks for the pointers - I like the 3 valves and it doesn't cost much more.

My requirements are much less lofty than yours. I have 2 5' strawberry towers with 100 plants each. The towers are filled with tapla's 1-1-1 mix (no organic/fertilizer present). The towers need daily watering (with the crushed granite, think hot concrete if allowed to dry) and daily fertilizing. I don't like my EZ-Flo injector, so I want to use/try a venturi.

I want the bypass in order to be able to (attempt to) get the right mix of fertilizer into the stream. That, and I must be crazy.

Since this is incredibly small scale (although I may want 2 since I have a tower of strawberries on the deck as well) I don't think I need 1" PVC - frankly the smaller the better if it works since I'm on drip into the top of two towers.

Attached is a picture of the 'demo' tube which is shorter and is on the deck. It is 8" inner diameter cell core PVC. The other two towers are in the garden at the back of the photo.

This is (obviously) a pre-planting picture. All was going well until my water timer broke last year and everything baked. So I reordered and refilled the towers again this year. I'll even remember to use fresh batteries (although that wasn't the problem)!


    Bookmark   April 22, 2014 at 9:15AM
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Ok, you definitely don't need as big of a set up as we have, but the principals are similar.

    Bookmark   April 22, 2014 at 10:59AM
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nil13(z21 L.A., CA (Mt. Washington))

The connection you are looking for to swap out the venturi (i think that's what you're referring to) is called a union.

You need three valves like Rio for a proper bypass. You need 2 valves to isolate the venturi. With those two closed and the valve on the mainline open the venturi is bypassed.

    Bookmark   April 22, 2014 at 11:27AM
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And the story continues.

A2Z Ozone sells a 1/4" venturi for about $10. Under the theory that smaller is better, this should help with the low flow (anyone want to correct me here?).

Now, since this is a 1/4" male connection, I would need a 1/4" female to 'standard' garden hose (male one end, female the other). What is the 'standard' connector for the hose end?

Does anyone have a Lowes/HD part number for this? I'm sure it exists, but is this a specialty type item?

Any thoughts?


    Bookmark   April 22, 2014 at 3:49PM
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Well, the eBay venturis arrived today.

The orange model on top in the picture is 3/4" and the blue is 1/2". I got 2 blues and an orange, and the orange was ordered with the hose and 'regulator'.

Each of the units is approximately 6" long.

From another thread, I understood the Mazzei 283 (their low flow model) to be much smaller than the 'China eBay' ones. Today I ordered a 1/4" unit from a2z ozone.

This was $9.99 delivered.

The orange (3/4") unit seems to fit a garden hose; the blue unit is much smaller - time to get some adapters. Surprisingly, the two units appear to be the same length. This should make the bypass with interchangeable venturis easier to build.

Let's see what size and surprises the 1/4" model gives me in the next few days.


    Bookmark   April 23, 2014 at 4:11PM
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Those Venturis likely use BSP threading. For example:

This is not going to work with NPT threading you find in the US. I'm not sure how you can adapt them, maybe with a gasket or something. hopefully someone else can help.

This post was edited by OttoGardener on Wed, Apr 23, 14 at 16:31

    Bookmark   April 23, 2014 at 4:30PM
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I'll check with my local plumbing supply store for 1/2" and 3/4" BSP to PVC adapters.

I've read the 1/2" BSP may be identical (or maybe it was 3/4") to NTP - and that it is JUST that size.

If I run to PVC I can then run back to a hose connector.

It's never easy.


    Bookmark   April 23, 2014 at 9:17PM
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Mine is identical to the orange one and it used a NPT fitting. I got the one with the rubber o rings in the bottom. Like I said take it to the store.

    Bookmark   April 23, 2014 at 9:23PM
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According to the eBay description, both my devices are BSP.

I can't find a local source for the converters, but found that Dura Plastics makes them (one of the people I called is a dealer for duraplastics, but doesn't stock these and only orders in case sizes). This in turn brought me to the company which gave me part numbers.

This brought me to the Northeast sales rep and the phone number for a local distributor - I'm waiting for his return call.

In the interim, google became my friend (see link below).

The part numbers I was given are, for the 1/2" and 3/4" respectively: BS435-005 and BS435-007. These parts go from the thread to a PVC slip.

Anyone think this is wrong before I order a few of these?

Additionally, size shipping is brutal, anyone want a few of these and I'll send them along after increasing my order size?


Here is a link that might be useful: 1-888-PVC-FLEX - BSPT fittings

    Bookmark   April 24, 2014 at 10:56AM
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