Okay, I want more water pressure. I bought two separate under-the-
sink water filters. Not a dual unit, but two self contained water
filter units. Now I want to hook them up so that water flows
separately through each, then joins back together again before exiting
the kitchen faucet.

The unit is housed with 3/8" FPT (plastic) holding a 3/8MPT to 1/4
compression male (plastic). Do I have to step it down to 1/4 or can I
use the 3/8" FPT? I'm wondering if putting too much pressure on the
unit (by not bottlenecking it to 1/4"C) will cause it to function
improperly. I don't care about the pressure in this regard. I'm
getting the increase by using two units instead of the usual one.
However, I do want to use less fittings.

What about exiting the units? If 1/4 C is the intake then that's the
bottleneck, so at that point it shouldn't matter if I use 1/4"C or
3/8" FPT, right?


The faucet I have in mind is a single handle with standard 1/2 MPT.

Anyone know if the units themselves automatically act as a back flow
preventer? If not I'd be worried unequal pressure might blow water
back and forth from filtered to unfiltered water, not that I can see
any terrible consequences.

advice or criticism welcomed
thanks

Jim Rainfordson wrote:

Okay, I want more water pressure. I bought two separate under-the-
sink water filters. Not a dual unit, but two self contained water
filter units. Now I want to hook them up so that water flows
separately through each, then joins back together again before exiting
the kitchen faucet.

The unit is housed with 3/8" FPT (plastic) holding a 3/8MPT to 1/4
compression male (plastic). Do I have to step it down to 1/4 or can I
use the 3/8" FPT? I'm wondering if putting too much pressure on the
unit (by not bottlenecking it to 1/4"C) will cause it to function
improperly. I don't care about the pressure in this regard. I'm
getting the increase by using two units instead of the usual one.
However, I do want to use less fittings.

What about exiting the units? If 1/4 C is the intake then that's the
bottleneck, so at that point it shouldn't matter if I use 1/4"C or
3/8" FPT, right?


The faucet I have in mind is a single handle with standard 1/2 MPT.

Anyone know if the units themselves automatically act as a back flow
preventer? If not I'd be worried unequal pressure might blow water
back and forth from filtered to unfiltered water, not that I can see
any terrible consequences.

advice or criticism welcomed
thanks

pressure will be maximum when the faucet is off, stopping down the fitting
will reduce your flow. When you open the faucet the pressure will drop as the
flow increases. So... if your filters can handle the pressure when there is no
flow they will be fine when there is a flow.
Also, the flow will balance out between the 2 filters, if one is more plugged
than the other the flow though the plugged one will be less. You wont get
backflow here, high side pressure will be the same on both units.You could
possibly get some micro drift when the faucet is off, but who cares, its
drinking water and it will only be refiltered agin when the faucet comes on.
The bottleneck will be the smallest ID, try to maintain the 3/8 if you can.
A short run of smaller ID has less effect than a longer run.
Seems to me, either you have a filter that doesnt have a very high
through-put(is it designed for this type of use?), a low pressure water
supply, or a plugged faucet/aerator.
Eric

"Jim Rainfordson" wrote in message
The unit is housed with 3/8" FPT (plastic) holding a 3/8MPT to 1/4
compression male (plastic). Do I have to step it down to 1/4 or can I
use the 3/8" FPT? I'm wondering if putting too much pressure on the
unit (by not bottlenecking it to 1/4"C) will cause it to function
improperly. I don't care about the pressure in this regard. I'm
getting the increase by using two units instead of the usual one.
However, I do want to use less fittings.

Larger is better. l It won't increase pressure, but it won't restrict flow.

What about exiting the units? If 1/4 C is the intake then that's the
bottleneck, so at that point it shouldn't matter if I use 1/4"C or
3/8" FPT, right?

Right



The faucet I have in mind is a single handle with standard 1/2 MPT.

Anyone know if the units themselves automatically act as a back flow
preventer? If not I'd be worried unequal pressure might blow water
back and forth from filtered to unfiltered water, not that I can see
any terrible consequences.

No, they do not, but I don't see that it would blow water back at any point
either. Where is the unequal pressure coming from? The hot water when
running a blend? Not a problem.

"Jim Rainfordson" wrote in message
...
Okay, I want more water pressure. I bought two separate under-the-
sink water filters. Not a dual unit, but two self contained water
filter units. Now I want to hook them up so that water flows
separately through each, then joins back together again before exiting
the kitchen faucet.

The unit is housed with 3/8" FPT (plastic) holding a 3/8MPT to 1/4
compression male (plastic). Do I have to step it down to 1/4 or can I
use the 3/8" FPT? I'm wondering if putting too much pressure on the
unit (by not bottlenecking it to 1/4"C) will cause it to function
improperly. I don't care about the pressure in this regard. I'm
getting the increase by using two units instead of the usual one.
However, I do want to use less fittings.

What about exiting the units? If 1/4 C is the intake then that's the
bottleneck, so at that point it shouldn't matter if I use 1/4"C or
3/8" FPT, right?


The faucet I have in mind is a single handle with standard 1/2 MPT.

Anyone know if the units themselves automatically act as a back flow
preventer? If not I'd be worried unequal pressure might blow water
back and forth from filtered to unfiltered water, not that I can see
any terrible consequences.

I am going to do the same thing, one of these days. Use the biggest pipe
you can for as long as possible. Won't help much, but maybe a little.

On 2008-07-07, Jim Rainfordson wrote:

Now I want to hook them up so that water flows separately through
each, then joins back together again before exiting the kitchen
faucet.

Sounds fine, it would be best to ensure the parallel paths are
identical, same length of fittings, etc.

The unit is housed with 3/8" FPT (plastic) holding a 3/8MPT to 1/4
compression male (plastic). Do I have to step it down to 1/4 or can
I use the 3/8" FPT? I'm wondering if putting too much pressure on
the unit (by not bottlenecking it to 1/4"C) will cause it to
function improperly.

I would be inclined to use the unit as supplied with the 1/4" fitting.
Increasing the pressure on the filter would increase the flow rate,
and it is possible this could decrease the filtering efficiency. You
could check with the manufacturer to see what they say.

What about exiting the units? If 1/4 C is the intake then that's the
bottleneck, so at that point it shouldn't matter if I use 1/4"C or
3/8" FPT, right?

No, that's not really true. The way fluid flow works with
pipes/fittings in series with a constant pressure source is that each
fitting will have a certain flow rate to pressure drop relationship.
The overall flow rate will be just enough so that the sum of the
pressure drops across all the fitting/pipes between the source and the
faucet will just equal the pressure of the source. So adding
additional lengths of small diameter tubing will cause additional
pressure drop and decrease your overall flow rate.

Yours, Wayne