[LazyPup]

I am totally amazed that you are even getting the trickle.

Pressure is by far the most misunderstood concept in all of plumbing. Most people assume that if they have 50psig at the main they will then have 50psig at the faucet or showerhead but such is not the case.

When all the faucets and valves are closed and there is no flow the pressure in the system will be at equilibrium with the supply pressure from the municipal main or home well pressure tank. This is known as “Static Pressure” or “At Rest Pressure” and it will be equal at all points in the system regardless of line size or elevation.

Once a faucet or valve is opened and flow begins the pressure in the system is influenced by a number of factors. First of all, a portion of the pressure in the system is being relieved by the amount of water discharging from the faucet to standard atmospheric pressure.

If the water makes a vertical rise from the source to the point where it discharges the flow is opposed by the physical weight of the water in the riser. This opposition to flow is known as “Vertical Static Head” and it is equal to .434psi per foot of vertical elevation. By example, consider a house where the water line enters the basement at floor level. We then have:

8’ Floor to ceiling.
1’ for the floor joists and flooring on the first floor.
8’from the first floor to the ceiling.
1’ for floor joists and flooring on the second floor
6’ from the floor to the showerhead.

24’ Total vertical rise.

The physical weight of the water in that riser is then 24’ x .434psi = 10.41psi

If we had 50psig at the water main the resultant pressure at the shower head would first be reduced by the weight of water in the riser which opposes the flow therefore the resultant pressure would be 50psig minus 10.41psi = 39.59psig.
Next we must consider “Friction Head”. Friction head is the physical opposition to flow caused by friction between the water and the inner walls of the pipes or eddy currents caused by directional fittings such as Tee’s and Elbows. Friction head is generally defined by an equivalent amount of “Vertical Static Head” thus if a line was said to have 20 feet of friction head it would mean that the opposition to flow is equal to a 20’ vertical rise or 20’ x .434psi = 8.68psi. This pressure is also in opposition to flow so it would also be subtracted from the supply pressure thus if we had 20’ of friction head in our above example the resultant pressure at the showerhead would be;

X = Supply pressure minus (Vertical Static Head + Friction Head)
X= 50psig – (10.41psig vertical static head + 8.68psig Friction Head) =
X= 50psig – 19.09psig
X= 30.91psig

This resultant pressure is known as “Dynamic Head” or the working head pressure at a specific point in the system.

This can be seen in the plumbing codes by example, The International Residential Plumbing Code requires a minimum “Static Head Pressure” at the main of 40psig but when we examine the “Fixture Supply Dynamic Head Pressure” chart we find that a shower is only required to have a flow rate of 3 gallon per minute at 8psig dynamic head.

When sizing water lines per plumbing code specification we first make a list of all fixtures in the structure that will be connected to the water supply. We then consult a table in the code that assigns a “Fixture Unit” value to each fixture, from which we can compute the total number of “Fixture Units” required by the structure.

We then measure the distance from the source to the furthest fixture and consult the line -sizing table to determine the required size of line.

Per code the minimum permissible line size is ¾”

Now let us consider your ¼” line.

When comparing the volume or capacity of different sized lines we cannot use diameter but rather we must use a formula that compares cross sectional area thus the formula is:

LARGE DIAMETER SQUARED divided by small diameter squared.
Where:
¾” = .75”
¼” = .25”
N= (.75 x .75) / (,25 x .25)
N= 0.5625 / 0.0625
N= 9

This means that a ¾ line has the same capacity as 9 lines at ¼” each or conversely your ¼” line has 1/9 the capacity of the code minimum ¾” line which no doubt accounts for why you are getting a trickle.

In addition, as the diameter of a line is decreased the velocity of flow in the line must increase proportionally however as velocity of flow increases the Friction head will also increase proportional to the velocity thus while you have 58psi Static Head Pressure once flow begins you have nearly zero Dynamic Head Pressure.