We’ve all heard the phrase “there is no stupid question except the unasked one”. I’m going to prove that phrase wrong.
We all have plugged a long hose to an outside bib that had a great pressure and flow. Man, it just gushes out. Then we plug on the hose and it just pisses out the other end. I know there’s friction and hose flex to deal with. Bernoulli’s equation, yeah right, maybe 40 years ago, but not now.
So now to the question, what happens to that “gush” that went into the hose (or pipe)? If you have 15 GPM going in, you should have 15 GPM coming out, but don’t seem to. Daaaaah
Replies
Are you serious about 15 GPM? That,s alot of water! 5 GPM is more
like what I would expect. Try puttting a 5 gallon pail under the spigot and time it with and without the hose. Sometimes, because of the constriction of the spigot it can seem like there are more GPM's than there actually are. If there is a big difference it's time for a larger diameter (and better constructed) hose.
Ya think 15GPM might have been an arbitrary number? :)
what happens to that "gush" that went into the hose (or pipe)?
It sure aint 15 gpm anymore. You had say 15 gpm and all the pressure drop was across the spigot, the gauge pressure in the gush is close to zero. You had "X" amount of energy leaving he spigot.
Now you hook up the hose, you have additional pressure drop in the hose (espec. if you leave it coiled and the water has to run around in circles and get 'tired out'.) You do not have the same flow anymore, but the amount of energy in the water flow leaving the spigot is the same, you have just lost a lot of it in friction and turblulence in the hose - the pressure out the end of the hose is again near zero, so the gush has to slow to maybe a trickle. This is grossly simplified, but maybe helps with visualizing conservation of energy.
Okay, we're getting hung upon my figures. I have a 2 inch, gravity, water line coming into my house with measured pressure of 55 psi. Because I don't use soap in the shower, I have an in-line booster to raise my pressure to around 70 psi. I want to calculate the water flow and pressures at the fixtures using different diameters of supply tubing.
I just don't understand that if you have 15 GPM going in a pipe (regardless if it's 1/2, 3/4, or 1 inch), do you have 15 GPM coming out, and if not, why?
If you have 15 gpm going in, you will have 15 gpm going out.
However, after you add the hose, you no longer have 15 gpm going in either - think of shutting off the faucet as the extreme case of a very long hose.
okay, I think I got it. thanks for your time and patients.
hey doc... how many patients did that advice cost ya???Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming<!----><!----><!---->
WOW!!! What a Ride!<!----><!---->
Forget the primal scream, just ROAR!!!
Junk explained the reasons.
But what is the end result your looking for?
Are you trying to size your system?
Do you look to the government for an entitlement, or to GOD for empowerment. BDW
your right, I'm just trying to determine what size pex to run to my various fixtures and what flow and pressure will result.
You are over analyzing the situation. Run 3/4" to the fixtures that you want better flow - like maybe the showers, and the kitchen sink. Run 1/2" to the rest. Don't run anything less than 1/2" regardless of what the manufacturer's sales strategy is. The thing is that since the Pex fittings fit inside the tubing, they restrict flow.
Since you are concerned about pressure and flow, if the service line is not already run to the house, run a 1".
Here is anther thing that might well enter into the equation. I'm guessing you are a DIY. At a lot of supply houses sell Pex (or similar brands) that comes only in 100' and 300' rolls. So, if you have to buy two 3/4" rolls to run 120' of 3/4" and a 1/2" roll to run 55' of 1/2", where is the savings?
Another thing along the same lines. A crimping tool costs around $125, so if you decided to use 3 tubing sizes, well....
Of course, if you are hiring a plumber, these last tow points may not come into play.
OK fair enough
Are you going with a manifold & individual lines to each fixture?
Or a main line with standard branches.Do you look to the government for an entitlement, or to GOD for empowerment. BDW
Will use a manifold, but I'm going to have a lot of stuff in there. A 2" line from water supply, a 1 1/2" sediment/UV filter rated at 15 GPM, in-line booster pump, radiant heating system with holding tank for domestic supply. I haven't figured out the order of things yet. I figure the boys at NRT will want some input on the layout.
OK first the heat is pretty irrelevent once it's full then demand for water is pretty much nonexistant.
Booster pump----- put a well tank with that so the pump is not cycling all the time.
If you're under 100' 1/2" will be fine.
Some big foo foo tub & shower valves like 3/4" though.
I run 3/4" to my hose bibbs.
My own rule I limit all 1/2" lines to 2 fixtures--- 3 fixtures then I go with 3/4"Do you look to the government for an entitlement, or to GOD for empowerment. BDW
Why not 3/4" for everything, what's the downside? Although I'll probably have some 1/2" left over from the radiant heat system.
No problem doing 3/4" it's just a cost matter.
If you're planning on using the left overs from the radiant heat make sure it is approved for potable water, & vise versa.Do you look to the government for an entitlement, or to GOD for empowerment. BDW
One problem with using large piping for domestic HW is that it takes longer to get to a distant faucet.
True, but that's what circ pumps are for.Do you look to the government for an entitlement, or to GOD for empowerment. BDW
Why not 3/4" for everything, what's the downside?
3/4" means there is a lot more cold or lukewarm water between the fixture and the water tank, so longer hot water waits.
Showers that have 2.5 gpm flow restrictors won't benefit.
Sinks that are fed by 3/8" riser lines will never see the difference (have you seen how small the orifice is inside the faucet?)
Big tubs need high flow faucets and 3/4" lines.
Treat every person you meet like you will know them the rest of your life - you just might!
The 15 GPM is what the sediment/UV filter is rated at with a 1 1/2 " inlet/outlet. None of my runs will be over 50 feet, exect for outside bibs. Shower restrictors don't concern me since I developed a spring for my water supply, half mile of trench 6' deep.
I think all showerheads are 2.5 gpm now, unless you doctor the flow restrictor with pliers...
My well pump will only pump 7.5 gpm, but my pressure tank is pretty big, so let it flow...
No shortage of water here either (30 gpm in the well) - I am thinking of putting in hot and cold hydrants outside the garage.
Treat every person you meet like you will know them the rest of your life - you just might!
Showers that have 2.5 gpm flow restrictors won't benefit.
When we 'fixed' the new shower head by prying out the restrictor, DW say 'AWL' right<G>
>> Sinks that are fed by 3/8" riser lines will never see the difference (have you seen how small the orifice is inside the faucet?) <<
So, based on your reasoning, any sink should only have 3/8" supply lines....
I never said that, but thats what the pex folks are trying to sell us. I am amazed at how much water can come through a line that small, but I plumb my houses w/ 1/2" pex anyway except for big tubs and outdoor faucets, which get 3/4".
It does seem a little strange to run a 1/2" line, then go way down to 3/8" at the sink, however.
Treat every person you meet like you will know them the rest of your life - you just might!
Eureka, that damn bulb finally lit in my head, thanks to junkhound and plumbbill. Thanks. That small opening in your fixtures will benefit from a larger supply tube to it simply because a larger supply tube will have less pressure loss and more water flow to force thru that fixture.
But, that brings up another question. If that flow restricter works by reducing the size of the orifice, could you not overcome that by increasing the amount of pressure? It stands to reason that a 2 1/2 GPM flow at 60 psi is going to be a higher flow at a 80 psi. If I'm right, you do benefit from a larger supply line. However, as was pointed out, there is a longer wait for hot water with the larger supply line.
Also, is there any reason I can't use left-over heating PEX for domestic supply.
With water, Pressure is the same as Voltage in eletricity; Pipe Diameter (R)is the same as wire gauge (R); Flow is the same as current (I).
E/R=IP/R=F
So, If you've got an electrical circuit with a big wire feeding a small wire feeding a lamp, the total resistance is Big wire (1 ohm) + small wire (2 ohms) + lamp (100 ohms) = 103 ohms.
In a water "circuit" with a big pipe feeding a small hose (under a sink) feeding a 2.5 GPM fixture, you've got Big pipe (1 Wohm) + small (2 Whom) + fixture (100 Wohm) = 103 Wohms.
Change the big wire or the big pipe to small and you only get a difference of 1 out of 103 ohms or Wohms. Not noticable. (Made up numbers for illustration, fantasy word "Wohm" stands for Water ohm.)
But, 300' of 14ga extension cord won't run your Skilsaw and 300' of 1/2" pipe won't effeciently fill your hot tub.
50' - 100' of 1/2" feeding an angle stop and 18" of 3/8" feeding a 2.5 GPM fixture might, maybe, possibly, cut your flow down to 2.49 GPM.
Pressure's like voltage, Measure the voltage at the end of 300' of 14ga with no load and you'll see 120V. Pressure at the closed end of 300' of 1/4" pipe will read the same as the main line pressure. No current. I*R=V; 0*R=0 loss.
Flow regulated fixtures have a soft plastic or rubber gizmo that makes them pressure sensitive. They close tighter with higher pressures.
PEX comes in flavors; Potable rated and non-potable rated, and oxygen barrior and non- oxygen barrior.
Water systems come in closed loop and open loop; Open loop regularly has fresh water added to the system.
An open loop system or a closed loop with non-oxygen barrior PEX must use rust resistant parts.
SamT
gotcha
Slight clarification, re:
Flow is the same as current (I).
Flow is analogous to current, but not the same. Recall from long ago analog computers that the 'resistors' used for running pipe flow problems varied in resistance according to the 1.8 power of current.
e.g P/R=F^1.8
Code books use something called fixture units.