Water Hammer Arrestors
Plumbing System Design
February 1, 2007
Controlling water hammer in a plumbing system is necessary as a way to reduce shock pressure and confine its action to the section of piping in which it occurs. This is the premise PM Engineer worked from when it surveyed its readers recently about their views on water hammer arrestors.
Did readers reaffirm the need for water hammer arrestors in current plumbing system design? The answer to that question was a resounding “yes.”
We sent questionnaires to 1,600 of our readers and a whopping 26% responded. In the area of marketing surveys, 26% is unprecedented. Usually, a response of 3% is considered to be very successful. So, again, thank you for your response and involvement in the industry. (A breakdown of respondents’ job titles and classifications can be found in Figure 15.)
What We AskedThis survey encompassed 14 questions broken up into three sections. Section one focused on what you use to control water hammer; section two on arrestor location and sizing; and section three on fixture fittings, plastic plumbing systems and plumbing contractors.
The first question we asked was: When designing a water distribution system, do you include a means for preventing water hammer (see Figure 1)? More than 98% of those responding gave an affirmative answer. We expected a very high response, but were a little surprised at the 98% figure.
For those who did include a means for preventing water hammer, we wanted to know how often they used air chambers to control water hammer (see Figure 2). Based on our survey-which did not distinguish between standard and calculated air chambers-just over half of plumbing engineers (52%) use air chambers sometimes, most of the time or always. At the other end of the spectrum, exactly one-third of those responding (33%) said they never use air chambers, and 15% said occasionally.
This was rather interesting since the model plumbing codes stopped recognizing the use of air chambers for controlling water hammer. Specifically, in the 2006 Uniform Plumbing Code (UPC), see Section 609.10 Water Hammer and 609.10.1 Mechanical Devices; in the 2006 International Plumbing Code (IPC), see Section 604.9 Water Hammer. The sections read as follows:
UPC Section 609.10 Water Hammer. “All building water supply systems in which quick-acting valves are installed shall be provided with devices to absorb the hammer caused by high pressures resulting from the quick closing of these valves. These pressure-absorbing devices shall be approved mechanical devices. Water pressure-absorbing devices shall be installed as close as possible to quick-acting valves.”
UPC Section 609.10.1 Mechanical Devices. “When listed mechanical devices are used, the manufacturers specifications as to location and method of installation shall be followed.”
IPC Section 604.9 Water Hammer. “The flow velocity of the water distribution system shall be controlled to reduce the possibility of water hammer. A water-hammer arrestor shall be installed where quick-closing valves are utilized. Water-hammer arrestors shall be installed in accordance with the manufacturer’s specifications. Water-hammer arrestors shall conform to ASSE 1010.”
According to our survey, many are using water hammer arrestors. Question three (Figure 3) addressed this topic specifically, by asking: How often do you use water hammer arrestors to control water hammer?
A significant number of readers (38%) said they always use them, and another 30% said they use them most of the time. Combined, these two replies equal 68%-more than two-thirds! There was a large drop off in readers who said they use arrestors either sometimes (19%) or occasionally (10%). And just 3% said they never use them.
The next question regarded how often participants’ designs included other concepts to reduce water hammer-such as short branch lines, oversized pipe (to reduce velocity) or reducing system water pressure (Figure 4). Based on reader feedback, it appears these concepts are not preferred.
Specifically, more than half the participants told PME they either never (27%) or occasionally (25%) design plumbing systems with these concepts. The largest number of readers (30%) indicated they sometimes use these concepts. A very small percentage (5%) always use them, and a small percentage (13%) use them most of the time.
The next question (Figure 5) asked readers if they considered water hammer to be a problem with commercial or residential systems. Overwhelmingly, the participants said water hammer is a problem in both types of systems (71%).
Not surprisingly, many more survey takers noted problems with commercial systems than with residential systems (24%, compared to 5%). This is reflective of PME readership, in general, which tends to design predominantly commercial and large residential systems.
Location and SizingSection two of the survey encompassed questions addressing issues related to location. Question six asked: How often in your design do you specify the location for each water hammer arrestor (Figure 6)? The replies weighed heavily in favor of always (35%) or most of the time (34%). Then, in descending order, came sometimes (15%), occasionally (11%) and never (5%).
[Editor’s Note: Of the 10 sliding scale questions in the survey, this was only the second one where the percentages decreased with each succeeding answer option (i.e., highest to lowest). The same type of result occurred with question three.]
Next came the question: How often do you require water hammer arrestors to be installed in an accessible location (Figure 7)? By a wide margin, respondents said “always” (56%). The next highest answer was most of the time with 24%.
On the low end of the spectrum, just 8% responded that they sometimes required such an installation-followed by never (7%) and occasionally (5%).
Question eight was: How often do you locate water hammer arrestors on the top of a riser rather than each branch line (Figure 8)? This detail is shown in many plumbing engineering books and papers on water system design. For the first time in the survey, the “sometimes” choice drew the largest response (35%) amongst the sliding scale answers.
Interestingly, the second choice by readers was never, with 25%. This was followed by occasionally (20%), most of the time (15%) and always (5%).
For question nine, we sought feedback on whether or not our readers use The Plumbing and Drainage Institute (PDI) Standard PDI-WH 201 (revised 2006) to determine the location of water hammer arrestors. According to the PDI, “the use of this standard is voluntary…and this standard is intended to provide a uniform measure of performance by water hammer arrestors.”
Based on our survey, readers are nearly split in their decision to use Standard PDI-WH 201 (Figure 9). A little more than half, 53%, say they do use it, while about 47% say they do not.
Question 10 closed out section two of the survey, asking: How do you size water hammer arrestors (Figure 10)? In light of the data from the previous question, we weren’t surprised to see that more respondents size arrestors according to manufacturers’ instructions (46%) than the PDI Standard (45%).
We also weren’t surprised that significantly fewer readers used other methods for sizing. These included: from experience (27%), engineering reference books (20%), pipe size (16%) and other (2%). Other methods receiving write-in mentions were co-workers and computer analysis, as required for fast-acting valves, contract drawing, contractor sizing, flow rates, MasterSpec, per code, specifications and supply fixture units.
Final SectionIn the last part of the survey, readers were asked two questions related to fixture fittings and one each related to flexible plastic plumbing systems and plumbing contractors. The first fittings-related question was: Do you consider all sensor-operated fixture fittings as quick acting and capable of water hammer? Exactly two-thirds (67%) of the respondents responded in the affirmative, with the other third (33%) saying no (Figure 11).
The follow-up question, number 12, was: How often do you consult the manufacturer’s instructions of fixture fittings for guidance in the need for water hammer arrestors? The number one response (Figure 12) was sometimes (30%), followed by most of the time (26%) and always (12%).
These numbers do not surprise us, in light of the fact that nearly half of the survey-takers said they size water hammer arrestors using manufacturer’s instructions (question 10). The other responses for question 12 were occasionally (17%) and never (15%).
Question 13 asked: How often are you concerned with water hammer in flexible plastic plumbing systems? Many technical papers written on water hammer indicate that flexible plastic plumbing systems do not require water hammer arrestors for most designs that are within the engineering parameters of the flow velocity. This question drew the most evenly balanced responses among the sliding scale options (Figure 13).
Twenty-three percent of readers said they were sometimes concerned and 22% were always concerned. Interestingly, 21% said they were never concerned and 20% said they were concerned most of the time. Meanwhile, 14% of respondents said they were occasionally concerned.
Our final question was: How often do you permit the plumbing contractor to determine when and where water hammer arrestors are required? Based on our survey, most plumbing engineers don’t feel comfortable handing off this decision to a contractor.
A whopping 86% of respondents replied never (33%), occasionally (26%) or sometimes (27%). Only 4% said they always give contractors this permission, while another 10% said they give this permission most of the time (Figure 14).
I’m sure you would agree that this was another fascinating PM Engineer survey. If you received the survey questionnaire and responded, our thanks for helping out. If you did not receive a questionnaire, keep an eye in your mail for the next survey. When you get it, take a few minutes to fill it out and send it in. You can help contribute to our next article.