Ask Me Help Desk - What does a clogged filter affect?

Hi all,

It is common knowledge that as a filter (whether undersink or whole-house) gets closer to replacement time, the water flow is adversely affected. What I would like to know is, what exactly is the clogged filter affecting: the PRESSURE (i.e. if there would be a booster pump on the outlet side of the filter, things would be as good as if there were no interference from the filter), the VOLUME (i.e. if there were more volume - such as if the line were teed, each branch connected to a separate filter, and afterward the two lines were teed back together - then things would be better), or BOTH?

Awaiting your reply,
Moishe

Quote:

Originally Posted by PalmMP3

Hi all,

It is common knowledge that as a filter (whether undersink or whole-house) gets closer to replacement time, the water flow is adversely affected. What I would like to know is, what exactly is the clogged filter affecting: the PRESSURE (i.e. if there would be a booster pump on the outlet side of the filter, things would be as good as if there were no interference from the filter), the VOLUME (i.e. if there were more volume - such as if the line were teed, each branch connected to a separate filter, and afterward the two lines were teed back together - then things would be better), or BOTH?

Awaiting your reply,
Moishe

There would be no pressure if there were no volume. You can not have pressure without the volume to back it up. Conversely you may have volume without pressure. To prove my point, Truck on down to the nearest river where you have unlimited volume and measure the pressure one inch below the surface.
Let's reverse the situation and see what happens. Let's pretend that you have a pump that produces 100 PSI but a well about to run dry. You'll have pressure until you run out of volume from the well to back it up. A clogged filter will cut down on both pressure and volume, but if the pressure forces water through the filter while running out of volume the flow soon stops.
So much for your booster pump theory. Bottom line. You must have both to make a water system work.
"if there were more volume - such as if the line were teed, each branch connected to a separate filter, and afterward the two lines were teed back together - then things would be better),"

Think about it Moshie, you're attempting to build a perpetual motion device. Getting more volume out of a gizmo then you put into it.
Teeing off the main with a constant draw going on will reduce the volume by one half in the branches. You can not get more volume out of the main then it already has.
Regards, tom

Quote:

Originally Posted by speedball1

There would be no pressure if there were no volume. You can not have pressure without the volume to back it up. Conversely you may have volume without pressure. To prove my point, Truck on down to the nearest river where you have unlimited volume and measure the pressure one inch below the surface.
Let's reverse the situation and see what happens. Let's pretend that you have a pump that produces 100 PSI but a well about to run dry. You'll have pressure untill you run out of volume from the well to back it up. A clogged filter will cut down on both pressure and volume, but if the pressure forces water through the filter while running out of volume the flow soon stops.
So much for your booster pump theory. Bottom line. You must have both to make a water system work.

Actually, my question was'nt really meant to be a practical one - I know that in real life, you need both. I asked it merely because I am trying to learn plumbing theory. I did not think for a minute that I could get away with a booster pump and no volume - that was only an example to express the concept of what I meant by "loss of pressure". What I meant was a theoretical question, like this: granted, the water will not flow well in a real-world situation; there will be little pressure and little volume. But why? In other words, which is the underlying cause here - is the loss of volume actually causing the loss of pressure, or vice versa? Or maybe neither? Is it because a clogged filter acts as if it were a narrower supply pipe (thus cutting down on volume, while the pressure would otherwise have no problems), or does it act like a PRV (but theoretically, the volume would be good, except that it can't get through the clogged filter fast enough)?

BTW I asked because attaching a pressure gauge to various hose bibs throughout my house (outside, boiler drain, washing machine, utility sink spout, etc.) did not seem to show much of a difference whether the filter was new or old, or whether the hose bib was before the filter or after. So I'm wondering: is the pressure indeed the same (and it's the volume that gets screwed up), or am I seeing things (or maybe my gauge is faulty)?

Quote:

Originally Posted by speedball1

Think about it Moshie, you're attempting to build a perpetual motion device. Getting more volume out of a gizmo then you put into it.
Teeing off the main with a constant draw going on will reduce the volume by one half in the branches. You can not get more volume out of the main then it already has.

I don't think you understood what I meant. I'll try a little ASCII art:

Code:

_________ Filter 1 __________ | | | | IN----------|tee tee|--------------OUT | | |_________ Filter 2 __________|

As you can see, I would not be trying to pull more volume than the main has. What I would be trying to do is splitting the main, and then putting it back together again - i.e. to ultimately end up with the same volume as I started (i.e. even though, like you said, each branch would get half the volume, they meet again - and half + half = whole). The only difference is that each half would go through a separate filter. So if the "narrower pipe" theory mentioned previously were true, then putting half the volume through one filter and the other half through another filter should result in less volume loss than putting the whole volume through one filter. Does that make sense?

Quote:

Originally Posted by speedball1

You can not get more volume out of the main then it already has.

Which, in fact, brings me to my next question: why do you sometimes see a 1" pipe feeding the meter, but after that the main is 1¼"? In fact, in one of my pluming books, there is a chart showing roughly how many fixtures various water main sizes can handle. The chart actually shows such a configuration (1" before meter, 1¼" after) as being able to handle more fixtures than a configuration where the pipes are 1" both before and after the meter. Why should it make a difference? I thought you can't choke more than 1" worth out of the pipe if that's the size before the meter, so how does making the pipe bigger afterward help?