A checkvalve does not effect pressure

"A checkvalve does not effect pressure"

Unless it is defective and not opening all the way.

If the only work done was the check valve, it could be defective, or debris may have gotten into it.

Maybe I'm using the wrong terminology. It's a spring loaded double check valve.
I was talking to one of the other contractors the other day and when I mentioned the pressure problem he said the valves can 'do a job on pressure'. So, thus my question.

All work was done at the same time and all the pipe/lines, except some connections, are wirsbo. The plumber came out a few weeks ago when it was making a noise, took it apart and said it was fine. Just a little air in it.
They're not much help in determining the pressure problem and say it's caused by the water softener. It does improve about 10psi when the softener is bypassed but there's still something going on.

Even if a checkvalve is defective and not opening it will not effect pressure, it will effect volume and force but not pressure

Ok, I think I understand now.

I guess we have a problem with both since gpm has also decreased dramatically. It averages about 2 1/2 gpm at the wash area. That may be typical shower flow, but it's not enough to wash off a tractor.

If we fill a bucket at the point were the water line enters the building we get about 15 gpm.........by the time it gets to the wash area and the outside spigot, it's 2 1/2 gpm.

Many people measure the static pressure at the point where their water line enters the structure and erroneously assume that the pressure should remain constant throughout the structure when the water is flowing, but such is not the case.

Static pressure is just what the name implies, the pressure when the system is static, or in laymen's terms, when the system is at rest with no flow. The moment flow begins the static pressure will instantly drop to "Dynamic Pressure" (working pressure), which is static pressure minus "Vertical Static Head Loss" and "Friction Head Loss".

Water physically weighs 0.434pounds per vertical foot column therefore if we pump water up hill we lose 0.434psi for each foot of vertical rise, and consequently, if the point of demand is lower than the prime mover, such as a house connected to a municipal main where the house is downhill from the connection, we would gain 0.434psi for each foot of vertical differential.

now while Vertical Static Head Loss is very simple to compute, "Friction Head Loss" (FHL) is another matter entirely. FHL is a loss of pressure and flow caused by the water physically rubbing the inside of the pipe walls and eddy currents or restrictions generated by fittings in the pipe run. If one wants to be technically precise they must have a list of all fittings in the pipe run, from the prime mover to the point of demand, then consult a "Fitting Allowance Table" to determine the fitting loss for each fitting. Fitting Allowances are expressed in the equivalent length of straight pipe that would represent the same friction loss. By example, the fitting allowance for a 1/2" copper 90deg elbow is .6ft.

For simplicity when estimating FHL the code allows us a shortcut. First we determine the actual length of all piping from the source to the point of demand, then multiply that length by 1.2 to compensate for fitting allowances and yield TDL (Total Developed Length).

Maximum volume of flow is determined by the size of the orifice in the valve at the demand point. Once we know the volume of flow and the TDL of the pipe we then consult a publshed Friction Head Loss table to determine the amount of pressure loss, which is either expressed in psi/ft or sometimes in psi/100ft. In addition to Friction Head Loss the table will express the velocity of flow for a specific volume in a given size of pipe. Velocity of flow is very important for two reasons, 1. the higher the velocity of flow, the higher the friction loss and 2. if the velocity of flow exceeds 12ft/sec in copper or or 15ft/sec in plastic pipe we end up with excessive pipe wall erosion, therefore the codes limit us to 8ft/sec in copper and 12ft/sec in plastic pipe.

To give you an example of how it all comes together, under the IRC (International Residential Code) the minimum allowable static head pressure at the water main is 40psi however according to the specifications on IRC Table T 2903.1 the minimum pressure for a hose bibb is 8psi with a flow rate of 5gpm.

When you add a conventional garden hose to that hose bibb, the friction loss in the hose is 2 to 3 times the friction head loss of an equivalent length of pipe. Adding to that, a hose nozzle and its easy to see why your flow is diminished.

Maybe Lazypup could write about check valves- the spring seated checks have a cracking (seat release) pressure rating and more restrictive flow than the flapper (swing) checks, but I am ignorant as to whether they comply with code as backflow preventers.

BTW, the softener can be bypassed if you're washing horses.

As i stated previously, the Friction Head insertion loss for a check valve is nearly negligible, however for those who still don't want to believe it I challenge you to look it up for yourself.

You can download a free copy of the Copper Tube Handbook in PDF at the following website:

http://www.copper.org/publications/pub_list/pdf/copper_tube_handbook.pdf

On psge 32 of the handbook you will find a Friction Head Fitting Insertion loss table that expresses the loss in equivalent lengths of straight copper tubing for the same size. If you check the table carefully you will see that tne insertion loss for a "check Valve" is the same as the loss for a single 90deg elbow and considerably less than the flow through the side port of a tee.

1/2" check valve = 2' ..1/2" 90el= 2'
3/4" check valve = 3' .3/4" 90el = 3'
1" check valve - 4.5' .1" 90 el = 4.5'
1-1/2" check valve = 6.5' ...1-1/2" 90 el= 6.6'

Note that the losses are expressed as equivalent lengths of straight tubing and when computing Friction Head Loss you must add these lengths to the actual length of the pipe to determine TDL (totasl developed Length).

Once you have the TDL and know the demand in GPM you can consult the Friction Head tables on page 30 in the handbook to determine the correct size of pipe.

For the record. PPFA (Plastic Pipe & Fitting Assoc.) also has free plastic pipe handbook download and that book will contain the tables and installation specs for each type of plastic pipe.

Thought I'd share this info I came across.

13.20.140 Pressure loss.

Double check valves assemblies shall have a maximum loss of ten psi and reduced pressure backflow assemblies shall have a maximum loss of twenty-four psi. (Ord. 1845 2(part), 2004).

"Thought I'd share this info I came across.
13.20.140 Pressure loss.

Double check valves assemblies shall have a maximum loss of ten psi and reduced pressure backflow assemblies shall have a maximum loss of twenty-four psi. (Ord. 1845 §2(part), 2004)".

You are correct....

But what you have is likley not be a 'check valve' type assembly at all.... it is likely a 'backflow preventer'...designed to keep contaminated water from the horse troughs from backflowing into your potable water supply.

Pressure loss can be significant using some types of backflow preventers....as you are witnessing.

Because of the high contamination potential of the connection, you likley have a reduced pressure principal backflow preventer and the reason you have such a high pressure loss.