By Gary Battenberg
Last month we talked exclusively about the problems associated with excessive water pressure and the control methods available to comply with manufacturers warranty requirements. This month, we will look at the other side of the issue and that is Inadequate Water Pressure. Let’s refer to what the 2009 Uniform Plumbing Code (UPC) has to say so that we are clear on what is approved.
“Whenever the water pressure in the main or other source of supply will not provide a residual water pressure of not less than fifteen (15) pounds per square inch (103 kPa), after allowing for friction and other pressure losses, a tank and a pump or other means that will provide said fifteen (15) pound (103 kPa) pressure shall be installed. Whenever fixtures and/or fixture fittings are installed that require residual pressure exceeding fifteen (15) pounds per square inch (103 kPa), that minimum residual pressure shall be provided.”
Using the same water chemistry we started with, we are just going to change the water pressure for this exercise and then we will delve into the inherent problems created for the optimum performance of the specified water treatment equipment.
Water Hardness……8 grains per gallon (136.8 mg/L)
Water Temperature…61º F (16.1ºC)
Water pressure………28 (1.98 bar 0r 242.5 kPa*) psig**
* kPa = kilopascal, a unit of pressure equal to one Newton of force per square meter. One thousand pascals equal one kilopascal (kPa); a kilopascal equals 0.145 pounds per square inch.
** psig = pounds per square inch, gauge.
In the interest of keeping this exercise simple, attach a pressure gauge to an outside hose bib and open the valve handle to obtain the static water pressure in the system. To determine the pressure drop in the system under normal household water usage, turn the hot and cold water on in the shower or tub and then record the water pressure indicated by the gauge. Next, with the tub/shower running, turn the hot and cold water on at the kitchen sink and then record the water pressure indicated by the gauge. Turn off the water. If the pressure drops to 19 psig (164.54 kPa), technically there is not a compliance problem. If the pressure drops below 15 psig (103 kPa), then there is a compliance problem and you will need to specify a booster pump system. Before you make any recommendations, I strongly urge you to contact the contractors’ board and inquire as to what they will approve for boosting inadequate water pressure.
Now comes the important part of the application process. This is where you can get into trouble very quickly and find yourself correcting a problem at your expense, in addition to dealing with customer frustration. Any type of filtration or softening system is going to create a pressure drop in the service plumbing. At 19 psig (130.5 kPa) with just the tub/shower running and no treatment in place, there is no compliance problem. Now add the pressure drop across the filter or softener between 6 and 8 (4.1 -.5.5 kPa) psig and the net residual pressure to the service plumbing is at 11 to 13 psig (75.5 – 89.3 kPa), well below the minimum allowable residual water pressure of 15 psig (1.06 bar). If you consider the additional pressure drop of running water at the kitchen sink, it is quite likely that the residual water pressure will be below 10 psig (68.6 kPa).
Looking at your water treatment equipment specifications, you will find that a typical residential softener can operate at pressures as low as 20 psig (1.4 bar). Most RO appliances stipulate a minimum operating pressure of 40 psig (2.8 bar) with a few of the more advanced RO systems and countertop products capable of operating at 30 psig (2.1 bar) @ up to 500 mg/L TDS.
The other problem with installing water treatment equipment in low water pressure applications is a commonly overlooked part of the installation that must be completely understood if you are going to be successful in a low-pressure market. The drain line configuration of an automatic backwash filter or water softener is the most overlooked, misunderstood and, in a lot of cases, the hardest part of an installation.
In our next installment, we’ll look at some typical installation diagrams and learn how to identify and troubleshoot low water pressure problems and how that relates to improperly configured drain lines. You will learn how to tune-up a system to make it work properly to avoid frustrating call backs and customer frustration. Stay tuned!
About the author
Gary Battenberg is Managing Director of Santa Fe, NM-based Good Water Company, Inc. He has 29 years experience in the field of water treatment processes, including equipment design and manufacturing utilizing filtration, ion exchange, UV disinfection, RO and ozone technologies. Battenberg is also a member of the WC&P Technical Review Committee. Contact him at firstname.lastname@example.org or at (505) 471-9036.