SUCTION ENTRAPMENT TESTS
LEIF ZARS
Rev. 6/24/99

GENERAL PARAMETERS OF TESTS

All Piping was 2" Schedule 40 PVC

Water flow was created by running two 2 HP pumps is series so as to provide the desired range of GPM as regulated by a discharge valve.

Water flow in GPM was monitored by a Dynasonics Ultrasonic Flow Meter.

Data was recorded by a Monarch Data Chart Paperless Recorder.

Input to the Data Chart was provided by a WIKA Tronic Pressure Transmitter.

All Data Chart input was from within the main drain sump.

Pressure sensitive pump control was achieved with a Mercoid Pressure Control activating a locking relay.

Some pump suction and discharge pressures were recorded but are not reported herein In as much as they are immaterial to the tests.

Main Drain blockage was performed mostly with a 3-3/411 by 1211 by 1219 foam block - and occasionally with a flexible 20 mil fabric reinforced plastic film.

Specified main drain covers were in place at all times.

When dual main drains were used they were spaced 31 apart with 211 PVC.

All data was plotted to the same scale throughout this report.

MAIN DRAINS TESTED

* Main Drain #6 Same as Main Drain #1 but was Mounted with not as much Flexible PVC Pipe.

* Main Drain #7 Same as Main Drain #1 but was Mounted with no Flexible PVC Pipe.

DESCRIPTION OF SUCTION GRAPHS

Left Scale - "Hg
Bottom Scale -Seconds
Plot - 1/50th Second Intervals
Top - First " Hg - Not Relevant
Top - Date and Time of Test

RELEVANT DANGER NUMBERS

2.2 p.s.i. - 5.08 Foot of Head - 4.48 "Hg

DESCRIPTION OF UNITS

It was decided to quantify the suction characteristics depicted on the graphs and to this end the area ("Hg by Time In Seconds) under the 4.48 "Hg (2.2 p.s.l.) line was calculated as perhaps representing some indication of the overall Intensity of the suction danger.

In further explanation of this It was felt that a short Instantaneous vacuum, even though exceeding the 2.2 p.s.l., perhaps would not be dangerous In as much as It provided release almost Immediately and therefore could not entrap and likely could not cause physical harm due to the flexibility of the human body.

For simplicity, this "quantity99 of suction Is Identified In this report as "Inch Seconds9l. One Inch Second representing 191 of vacuum In excess of 4.4891 for I second, I.e.: 5.4891 for I second would be noted as "one Inch Second".

NORMAL DRAIN EVALUATIONS

#1 Main Drain - No Vent
Rated at 80 GPM
Entrapped at How rates of 62 to 80 GPM
Removal effort - Foam in excess of 31#
    Tests #1 & #2
Film Pealed with 5# Pull
    Test #3

#2 Main Drain - No Vent
Rated at 108 GPM
Entrapped at How rates of 108 GPM
Removal effort - Foam - Would not block off
Film Pealed with 10 to 15# Pull
    Test #4

#3 Main Drain - No Vent
Rated at 148 GPM
Entrapped at How rates of 62 to 109 GPM
Removal effort - Foam - Would not block off
    Test #5
Film sometimes bounced off Pealed with I5# Pull Test #6

#4 Main Drain - No Vent
Rated at 108 GPM
Entrapped at flow rates of 60 to 105 GPM
Removal effort - Foam sometimes bounced off (65.55 Inch Sec)
    Test #7
Film Pealed with 15# Pull
    Test #8

#5 Main Drain - No Vent
Rated at 252 GPM
Entrapped at flow rates of 106 GPM
Removal effort - Foam
When stuck removal by hand almost impossible Test #9
Film Pealed easily from corner Test #10

#6 Main Drain - No Vent
Rated at 148 GPM
Entrapped at flow rates of 63 to I IS GPM
Removal effort - Foam Sometimes bounced off (12.23 Inch Sec)
    Test #I I
Sometimes Stuck Test #12

DUAL MAIN DRAINS

#6 Main Drain & #3 Main Drain - No Vent
Rated at 80 GPM and 148 GPM

At 118 GPM #6 Main Drain was blocked with Foam which left 100% of the flow through #3 Main Drain. The suction encountered under #6 Main Drain peaked at 5.911 Hg - Test #13 Indicating 0.14 Inch Seconds, and leveled off at between 211 and 311 Hg when Foam captured - Test #14 - Indicating 0.17 Inch Seconds.

VACUUM CUT OFF SWITCH

Vacuum Mercury Cut Off Switch

A vacuum mercury cutoff switch with latching relay was assembled from commercial components and set to trip at Oll Hg.

Tests conducted Individually with #1 and #6 Main Drains at flow rates of from 60 to 62 GPM Indicated vacuum time curves raqnging from 24.88 Inch Seconds to 60.07 Inch Seconds with an average of 41.06 Inch Seconds - Typical Test #15

SUCTION LIMITING LOOP ("VENT") TESTS

Tests were conducted on 3/4" and 2" vents while using 2" PVC Main Drain Suction Lines. The 3/4" Vent was tested at a 42" depth and a 5611 depth,, while the 2" Vent was tested at a 56" depth only. Flow rates were from 42 to 56 GPM with the 42" depth Vent.

The 3/4" Vent at 42" depth showed two characteristics. One with some flexible PVC pipe In the suction system and the other without this flex PVC.

Tests with the flex PVC indicated a series of vacuum dips where as the ones without the flex PVC had only one major dip. The more rigid Installations averaged only 0.16 Inch Seconds whereas the flexible PVC Installations had a typical 6.29 Inch Seconds.

In general lnground swimming pool Installations would represent only the non flex condition since even If flex PVC were used it would be firmly held In place by concrete/gunite or the earth.

Typical of the flex graph Is Test #16. Typical of the non flex graph Is Test #17.

When the 3/4" Vent was located at a 56" depth flow rates could be Increased ranging from 61.5 to 78 GPM.

The Inch Seconds differed only slightly between the How rates (I % to 14%) however the difference between the #7 Main Drain (no flex) and the #6 Main Drain with flex showed the #6 Main Drain to have 296% more Inch Seconds.

This would indicate the necessity for rigid piping and fixtures in test work to produce field comparative results.

Typical graph of #6 Main Drain is Test #18. Typical graph of #7 Main Drain is Test #19.

Tests with a 2" Vent set at 56" and flow rates between 60 and 78 GPM indicated that the flexible piping to the #6 Main Drain as compared to the rigid #7 Main Drain showed an average of 3.40 Inch Seconds as compared to 1.62 Inch Seconds. Again showing the importance of rigid piping and fixtures to replicate field conditions.

Typical graph of #6 Main Drain Is Test #20. Typical graph of #7 Main Drain is Test #21.

Further tests were run with a "Vacuum Eliminator". A device intended to remove from the contractor any real control over the design and installation of the "Vent". Pipe sizes and dimensions are captured In the unit so as to produce a consistent degree of protection. See Drawing A.

This device when flowed at 62 GPM produced an average of 1.58 Inch Seconds, and when attempted forced closure of the drain produced an average of 2.86 Inch Seconds - quite similar to the 2" Vent set at 56" depth.

Typical graph of Vacuum Eliminator in Normal Mode is Test #22. Typical graph of Vacuum Eliminator In Forced Mode Is Test #23.

SUMMARY OF RESULTS

#1 Main Drain No Release

#2 Main Drain No Release

#3 Main Drain Occasional Bounce Release 13.1 Inch Seconds

#4 Main Drain Occasional Bounce Release 70.81 Inch Seconds

#5 Main Drain No Release

#6 Main Drain Occasional Bounce Release 12.23 Inch Seconds

Dual Drains    Suction peaked at 5.911 Hg and leveled off
    between 2" and 3" Hg and averaged 0.15 Inch
    Seconds.

Mercury CutOff Averaged 41.06 Inch Seconds

3/4" Vent @ 42"
    Rigid    0.16 Inch Seconds
    Flex     6.29 Inch Seconds

3/4" Vent @ 56"
    Rigid    1.91 Inch Seconds
    Flex    5.67 Inch Seconds

2" Vent @ 56"
    Rigid    1.52 Inch Seconds
    Flex    3.40 Inch Seconds

Vacuum Eliminator
    Normal 1.58 Inch Seconds
    Held    2.86 Inch Seconds

COMMENTS

It was determined that In order to record accurate suction pressures under the Main Drain Grate that the recording equipment be equalized to read zero when fully connected to the Sump before flow Is started.

If a vacuum gauge alone is used to record this information it will not Indicate the positive pressure head on the Main Drain from the water above It. It will merely carry a positive undisplayed pressure which must first be neutralized by a negative pressure equal to the height of the water over the recording point take off thus rendering erroneous numbers by the feet of this head.

Sta-Rite Ant!Vortex Main Drain 7017-0741 rated at 60 GPM was not tested in as much as it's 100% side slot entry would preclude body coverage even with the film we used on some tests. Further, this work was not intended to evaluate Main Drains without covers In place.

A conversion chart from Ft. Head to "Hg to PSI is included for convenience in this report.

A slightly revised copy of my earlier report on "SWIMMING POOL SUCTION HAZARDS" Is also Included In this report.

Main Drain #1

Main Drain #2

Main Drain #3

Main Drain #4

Main Drain #5

STA-RITE ANTI VORTEX MAIN DRAIN 07010-0741

DYNASONICS ULTRASONIC FLOW METER

MONARCH PAPERLESS DATA RECORDER

WIKA TRONIC PRESSURE TRANSMITTER

MERCOID PRESSURE CONTROL

12" X 12" FOAM BLOCK

20 MIL REINFORCED FILM

TEST BLOCK

DUAL MAIN DRAINS

2" SUCTION LIMITING LOOP

3/4" SUCTION LIMITING LOOP

VACUUM ELIMINATOR