Water pressure

[Pjskinner]

I know this subject has been beaten to death... But here it goes I had recently installed a new bath tub, valve and tub surround. When I changed over the valve I went with a "Flow Control" brand carried by sutherlands; Well when I installed it I changed the supply lines to it only due to the fact that it changed the height of the valve. Well when I changed them I used 1/2" cpvc for the hot and 1/2" for the cold. I noticed that the cpvc was smaller than the pvc so I asked the guys at the hardware store if this would affect anything and he said no. Is this my problem? Because when I take a shower I dont feel like the pressure is what it used to be. Please help I looked through all the archives to save the trouble but did not find any similar problems..


Thanks,
Pj

[LazyPup]

I would have to agree with the guys at your hardware store, there is not enough difference in the size of the two pipes in question to make any significant change in either volume or pressure.

All pipe is manufactured to a very exact set of standards that are set forth by the ASTM (American Society of Testing & Materials).

by ASTM standards Steel pipe is classified by its actual inside diameter measured in inches, therefore a 1/2" black iron pipe would actually measure 0.5" inside diamter. (Galvanized steel pipe will measure slightly less because it is determined by the size of the basic iron pipe before it undergoes the galvanizing process.)

Plastic pipes are manufactured to "Nominal Trade Size", which means that although the true size is slightly different, it would have the same volume characteristics of a steel pipe of equivalent size.

Pipe commonly used in residential applications is made in 1/4", 3/8", 1/2", 3/4", 1", 1-1/4", 1-1/2" 2", 2-1/2", 3", 4", 6", 8"

To most people it seems odd that pipe would be made in so many odd fractional sizes but we must understand that when comparing the volume of a pipe we cannot compare diameter but rather we must compare cross sectional area therefore in order to compare sizes we must use the formula:

LARGE DIAMETER SQUARED divided by small diamter squared. By example, let us examine a 1/2" diameter pipe compared to a 3/4" diameter pipe.

(3/4" x 3/4") / (1/2" x 1/2")=
(.75 x .75) / (.5 x .5) =
0.5625 / 0.25 = 2.25

As you can see, while there is only a 50% increase in diameter the volume increases 2.5 times.

In fact, in all cases increasing a line to the next larger trade size will approximately double its volume.

The basic rule of thumb is that if you double the diameter you will increase the volume by four times, by example, let us compare a 1" pipe to a 2" pipe.

(2 x 2)/(1 x 1)= 4 / 1 = 4 or an increase of 4 times the volume.

You state in your post that your original pipe is 1/2" PVC.


PVC PIPE ASTM D1785
1/2" nominal
Schedule 40
Outside diameter 0.840
Inside diameter 0.602

CPVC PIPE ASTM F441
1/2" Nominal
Schedule 40
Outside diameter 0.840
Inside diameter 0.602

As you can see the standard is the same for both PVC and CPVC pipe however the CPVC commonly sold in the hardware and home supply stores is technically not pipe, it is CPVC type CTS which means it is CPVC material manufactured to CTS (Copper Tube Size) rather than steel pipe size.

CPVC-CTS is manufactured to ASTM D2846 which lists the following:

CPVC-CTS
1/2" nominal
Outside diameter 0.625"
Inside diameter 0.469"

The PVC pipe has an ID of 0.602" while the CPVC-CTS has an ID of 0.469" for a total difference of 0.133"

Now, while this is a significant difference in pipe size, it must also be remembered that the internal ports in the mixing valve are typically only about 3/8" (0.375") therefore the short length of CPVC pipe still remains considerably larger than the internal ports and should not be a significant factor in the output volume of the shower head.

At this point a couple questions come to mind.

1. Have you examined the input port of the shower head to see if there is a flow restrictor or any debris that may have got lodged in the port during the repairs?

2. During the installation did you carefully deburr the ends of the pipe when you cut it? If not, there could be fragments of the pipe in the mixer internal ports and valving mechanism.

3. How did you make the transition from PVC to CPVC?

[Pjskinner]

1. Have you examined the input port of the shower head to see if there is a flow restrictor or any debris that may have got lodged in the port during the repairs?

Yes sir I did. There sas no debris on the screen but I cleaned it any way.I also let the wather flow from the shower portion with the head removed...

2. During the installation did you carefully deburr the ends of the pipe when you cut it? If not, there could be fragments of the pipe in the mixer internal ports and valving mechanism.

Yes sir I made sure to debur everything. When this problem came about I turned the main water off, then took the valve apart; and had someone turn the water on to flush the ports out.. Was this a good idea?



To clarify a little more on the transition I went from galvanized to pvc(cold)/cpvc(hot). Each side aprox. 5' in length.


Also the pressure for the tub faucet sucks to FWIW[xx(]


Thanks for the reply

Pj

[SSN596]

First, there is a significant difference between 1/2" NOM copper, and 1/2" CPVC. The CPVC typically used is CTS, and due to wall thickness is significantly smaller. However, you have a short section, and the problem is more likely that your shower valve has a flow restrictor in it. Also, if your shower head is new, it is low flow, and maybe your old one wasn't.

[Pjskinner]

quote:Originally posted by SSN596

First, there is a significant difference between 1/2" NOM copper, and 1/2" CPVC. The CPVC typically used is CTS, and due to wall thickness is significantly smaller. However, you have a short section, and the problem is more likely that your shower valve has a flow restrictor in it. Also, if your shower head is new, it is low flow, and maybe your old one wasn't.

Okay if the valve has a restrictor on it is there any way to take it out??