Great website - been reading for several months. Many excellent posts and answers.

I have a 10 acre lake with an 8" siphon as a primary. Current Watts lug style butterfly value leaks when charging the system enough to consider replacing. Found a PVC version for ~$250 as opposed to steel Nipco for $350 and Watts at $275. The PVC is rated for 150 psi. Can not find the specs on the current Watts valve, which was installed in 1988 (and does not have a rebuild kit). The drop is ~40' over an 80' discharge. Am I correct in assuming a 150 psi rated valve is adequate?

The hydrostatic pressure of fresh water is 0.43 psi per foot.

The "pressure" that the valve will experience is based not on the drop of the siphon run, but rather on the height of the water in your pond.

If your water level is 50' above the height of the valve, then the hydrostatic pressure on the valve is only 21.5 psi. (50 feet x .43 psi/foot)

However, water running down a siphon with a 40' drop also has velocity and great inertia. If you close the valve suddenly while the siphon is running full open, then the valve will get hit with some severe "water hammer" forces. These forces get very difficult to calculate very quickly.

I believe closing the valve gradually when you shut off the siphon will be the biggest factor in giving you long valve life. Gradually reduce the flow to a trickle, then close the valve firmly.

I believe the other possible error, would be closing the valve 95% (or some other nearly closed number) and having all of the water run through the very small remaining area and eroding the seals in the valve.

Good luck on your project. Hopefully you can get a person that runs lots of butterfly valves to respond as regards best practices.

Rod

I think 150 psi rated valve will be enough for you, but I would still consult with more experienced people who know everything about valve pressure and so on.

Any 8" valve will be expensive, but the Valterra stainless slide gate valve is effective and the least expensive. I use Valterra valves in every freeze/break proof siphon system I install for clients. The air break is the only place I install a valve, so the siphon can be manually started. At the outlet, a "test plug" is used if needing to prime, and is FAR cheaper than a valve!

RAINMAN!!!! Welcome back! We really missed you and your expertise and are glad you are still here.
There was a flurry of happy birthday wishes for you a few weeks back. Happy Birthday and keep us posted on how you have been doing.
Any new pictures on successful projects of late?

Thanks for helping NCDan out as well too!

I tried posting a picture, but the file was too big...and TY for the welcome back!

Throw the picture on imgur and then you can post it hear easily.

Like this?

No, like this:




Look at your "posts" on Imgur. Click on the pencil in the upper right corner. Then click on the 3 dots in the upper right corner. It will open up a drop down box that says "share options". Click on BBCode (forums) then just paste that in the post. What you paste has to have the .jpg at the end. Then the picture shows up automatically

LOL..I did copy and paste the BBCcode...Thanks for fixing it

Now can you explain what we are looking at in that wonderful picture?
I never saw large PVC pipe with the lattice pattern like that (in the background). Is that a custom order or does some get to freehand all that cutting with a jigsaw?? I guess that acts as a 'trash guard' on the intake side of your siphon?

And the valve in the middle of foreground and the other vertical pipe with all little holes in it, is that the air intake and always stays above the highest water level line?

The "lattice" is the inlet strainer. It allows sediment and moderate size debris that can't get stuck in an elbow to be removed, and also prevents any one area having high suction that could cause a clog. I cut it on-site with an electric chainsaw in a way that allows water flow from the top and sides, without risk of the pipe sucking out the supporting sediment and digging a hole/breaking off under it's own weight (14#/ft). When not in siphon mode, anything stuck, can float out...Makes it as close to clog proof as is posible. The valve is on the air break, and the pipe with "holes" in the top cap allows air to enter the system to break the siphon, yet brings all parts inside the dam, and below the frost line so the system is freeze proof. An external air break that typically extends out and over the water is notorious for getting broken, either by something hitting it, or in cold climates, ice lifting and busting the pipe...That style air break also gets easily clooged by mat algae and leaf/stick litter, which causes the air break to fail and the sipho to over-drain the pond.....By moving everything inside the dam, and below the frost line for any climate, my design can be installed anywhere, and is virtually fail proof and maintenance free....the only visible indication of the entire system, is a landscaping access cover similar to those used for lawn irrigation controls. To my knowledge, I am the only person that has designed and installs a siphon system like this, so I don't want to show just how I accomplish everything below grade. The seals are rated for a 100 year longevty and allows for some flexibility, so it won't break from water hammer or soil shifting

[img]https://i.imgur.com/DRIGBqA.mp4[/img] Click link to view a "test" run

Impressive to say the least, Rainman.

Looking good Rex!

Wonderful Rex! Thanks for the pictures and explanation! Certainly there is no need to disclose the things that make your skills and services unique. Congratulations on being really good at what you do. I'm sure your clients appreciate the design advantages as well.

Thanks for the props guys!

Rex, I'm late to the party, but glad to see you back.

Ditto