Working with pvc

[trilinearmipmap]

Well thanks for the help and advice, there are a lot of different opinions, I will take what makes sense to me and go with it.

[trilinearmipmap]

Can someone explain to me the difference between "standard threaded bulkhead" and "double threaded bulkhead"?

[IslandReefer]

Hi JimE
Is the flex PVC you are talking about, what they call spa flex, clear with diamond shaped mesh in it?
You say that you can use normal fittings, primer but the glue is different.
Can you tell me specifically what glue? Most if not all the flex fittings I have seen are held on with hose clamps.Avoiding the steel clamps, but getting a reliable joint would be great.

[yifan917]

I personaly would not use vasaline in the dry assembly as this is a greese that you have to remove prior to gluing. Just dry fit your parts they are never that hard to take apart.

Man, I really had a hard time to take them apart.... you guys must be so much stronger than I am......if not vasaline, use something else then.....but I personally don't think a little bit of vasaline is that hard to remove tho....

[StirCrazy]

Originally Posted by IslandReefer

Hi JimE
Is the flex PVC you are talking about, what they call spa flex, clear with diamond shaped mesh in it?.

flex pvd (spa flex is a commen name for it. it is white and it looks ribbed. go to any hot tub place and they sell it. except i was told to use the same glue as you do for regular PVC with it by the people who use it all the time (hot tub builders)

the stuff you were thinking about is reenforced vinal tubing.

Steve

[JimE]

Can someone explain to me the difference between "standard threaded bulkhead" and "double threaded bulkhead"?

That's a bit of a gray area, depends on the suppliers terminology. Double threaded should just have female threads on both the "inside and outside of the tank". Std would only have a female threaded connection "outside thetank" and just a smooth bore inside.

what they call spa flex, clear with diamond shaped mesh

No, spa flex is solid white with a spiral wire (plastic). The proper cement (in the common weld-on brand) is #795. This is good for flex-ridgid and IME I haven't had any problems with ridgid-ridgid in low pressure applications. On a side note, most spaflex will also take and inside barb fitting and ss clamp.

except i was told to use the same glue as you do for regular PVC with it by the people who use it all the time (hot tub builders)

"the same glue" could be any number of products. There is a weld-on 747 Pool 'R Spa that is rated for both, but it is usually hard to find and is more expensive than 795. What I would call regular PVC cement is 704 or 705 and it is not suitable for flex. The flex glue is more flexible because of course, flex flexes..... As far as advice from hot tub builders, think brain cells vs glue and resin fumes.....

Jim

Jim you sound like you know what your talking about but sweeping elbows make a significant difference in my opinion, not only can they flow up to 30% more water with the same plumbing scematics but they also will usually save you about 20% in eletrical costs by reducing the friction.

Here are some examples:

Two elbow types and three pipe sizes were used to illustrate the importance of correct plumbing.
Study the results below to understand these principles:
Elbows vs. Sweeps
Flow vs. Pipe Size
Vertical Head vs. Total Dynamic Head (TDH)
Pumping Cost vs. TDH
NOTE: Centrifugal Pumps (not self priming) perform best with flooded suction (pumps filled by gravity) as shown. The suction pipe should be nonrestrictive. To control pump’s output, put a valve on the discharge side.

Friction Loss in PVC Pipe
From the chart at left, using gpm and pipe size, find the friction loss per 100' of pipe.
Example: 40 gpm in a 11/2" pipe = 10' loss per 100' of pipe. 40' then causes about 4' of head loss.
Next find the friction loss caused by the fittings. Please note that the friction loss depends on the fitting diameter. A standard 1.5" elbow is equal to about 4' of pipe; long elbows, sweeps, and 45° elbows are equal to about 2' of pipe; straight through a “T”, about 3' of pipe; and a 90° turn through a “T”, about 9' of pipe.
Example: 40 gpm through 5 standard 1.5" elbows = 20' of pipe, which equals 2' of head loss. Add this to the pipe’s head loss and the actual vertical head height in feet to get Total Dynamic Head (TDH).


Hopefully this helps a few folks out...

edited for accuracy

[JimE]

There is a point when friction loss is at its peak performance in pvc pipe sizing, after that you are adding extra water volume that is heavy and will cause additional head loss as the weight of the water is pushing down on your vertical pipe runs.

Uh, still no. I'll give you a visual. Three cylindrical tanks 23ft tall with identical pumps screwed directly into the bottom. 1st tank is 2"diameter (pipe), 2nd is 12"dia, 3rd is 10'diameter. Say for example, the pumps have a max head of 15' - all tanks would fill to the 15' level right? Ok, now you stick on 3 pumps with a max head of 40' - all tanks will completely fill and overflow at the exact same gpm (ignoring the friction loss in the 2"pipe). How can that be when the weight of 500,000 lbs of water in the 10' tank is pushing down on the pump? They all are pumping against 23' of head. If you stuck a pressure guage on the bottom of each tank there would be 10psi on all three. The situations are identical and the "weight" of the water has absolutely no bearing on the performance. And remember that pressure (or weight as you call it) is omnidirectional - it is distributed in all directions, not all of it directly down into the pump. Now does it make sense?

Jim


[/quote]

yeah that makes sense, sorry bout that, dont know where my brain was there. Too much yard work, lack of oxygen to the brain I reckon....lol I believe I was confusing "backpressure" with headpressure.... opps, of course there would be less restriction using larger diameter pipe, if anything, the excessively oversized pipe would increase the head foot limit of your pump, as the pump curves and stated head limit are based on backpressure which decreases with larger diameter pipe. only problem you could run in to with dramatically oversized pipe is that you would be operating your pump at its peak running capacity, you would want to create a little extra backpressure at the discharge with a ballvalve so as not to burn out your pump prematurely...
But I do think that the sweeping elbows make a big enough difference in my books, and wallet.

"Now to remove my foot from my mouth...."gota get off the crack....

[trilinearmipmap]

I just checked out my local building supply store and all they have is ABS fittings so next time I'm down in Vancouver I'll pick things up, is Home Depot a good place to get everything all at once or should I head to a specialty plumbing supply store? I will need to buy some 1" and 1-1/2" pvc and elbows, T's, etc as well as the PVC primer and glue.