Chlorine Gas Injection – Safe Design Practice

Despite the many hazards, gas chlorine is still an established method for swimming pool chlorination. Chlorine gas is pulled from a pressurised cylinder under vacuum through supply lines. This is the safest way to feed gas chlorine, any break in the gas line results in a loss of vacuum instead of a dangerous pressurised gas leak.

Vacuum is created by water passing through the injector nozzle. The design of which accelerates the water to create a venturi effect that pulls chlorine from the vacuum regulator. The regulator is typically mounted directly on a pressurised gas cylinder. Most installations use two cylinders, with an automatic switch over mechanism for uninterrupted gas supply. A two cylinder system can be set up with multiple flow meters (rotameters) to supply one or several pools from the single source.

Note: The term ‘injector’ is used by some manufacturers, others use ‘ejector’. For simplicity we will use the ‘injector’ to cover all makes/models of gas chlorine injection products.

A vacuum based feed system has the potential to pull chlorine when unintentional vacuum conditions are created in system plumbing. This siphoning effect is most likely to occur when the circulation system plumbing is above the pool water level. A loss of line pressure can result in the lines draining out to the pool (or open filter tank), and the action of this water ‘falling’ out of the pipes can create enough vacuum to pull chlorine gas from the regulator. This high rate dosing of chlorine without water flow is very dangerous; small basins of water can easily be over chlorinated or pure gas can end up in areas where staff and patrons are not expecting it.

Alberta building code requires anti siphon features on chemical dosing equipment installed above the swimming pool. We highly recommend that all swimming pool gas chlorine systems use ‘anti-siphon’ injectors. This feature on an injector means that a vacuum condition will only draw chlorine if there is the presence of water flow & pressure on the injector. Installations with the potential for extreme vacuum (>24” hg) may require an additional vacuum breaker on the plumbing system.

Sample Injector Installation

We recommend one of the following injectors:

• Capital Controls EJ17 Ejector with Anti Siphon Valve Assembly (cannot be used with Evoqua regulators)
• Evoqua S10K Anti Siphon Chlorine Injector (can be used with Capital Controls & Evoqua regulators)

Recommended injector installation practices

1) Pressure gauges on the influent & effluent side of injector greatly assist troubleshooting
2) Inline strainer before the injector
3) Check valve installed on effluent water line (viton or teflon seals recommended)
4) Solenoid or booster pump control should prohibit rapid on/off cycling. Using both a solenoid and booster pump should be avoided.

5) Injector plumbing should be with rigid PVC pipe and unions for ease of maintenance. Flexible plumbing connections can deteriorate and are more likely to leak

Annual Maintenance Recommendations

1) Both manufacturers recommend annual preventative maintenance with designated PM kits
2) Clean the internal nozzle openings
3) Replace check valves that are downstream of the injector
4) Follow manufacturer recommendations for startup and equipment testing upon re-installation


De Nora Water Technologies Gas Chlorination of Swimming Pools Sept 2015
Do Nora Water Technologies Instruction Manual —EJ17 Ejector Sept 2015
Wallace & Tiernan Products S10K Chlorinator for Swimming Pool Installations Nov 1999
Photo Credit

SVRS Testing

SVRS (safety vacuum release system) and Automatic Pump Shut Off devices provide a layer of anti-entrapment protection for pools that don’t have multiple submerged suction outlets.  These devices are designed to disable pump suction (mechanical or electrical disconnects) in the event of a detectable entrapment.  There are several approved devices on the market, it’s important to familiarize yourself with the operation of your specific device.   Most devices require a system test is performed at the initial start-up and anytime system changes are made.  Depending on your device, there may be a requirement to perform periodic function tests to ensure your device is maintains its compliance with the ANSI/ASME A112.19.17 standard.  We strongly recommend you carry out and log periodic testing as it is a practice that many health inspectors are looking for during onsite inspections.   Some pools with multiple pumps may have multiple SVRS devices, it is important to test each device.  Should your device not function as designed during a test, it is very important to close the pool to bathers and carry out additional troubleshooting to resolve the issue.  We can set this service up as a recurring visit with our Evaluator™ program or provide additional training to ensure your team is confident with their SVRS operation and testing procedure.  It’s very important that all staff at your facility are aware of potential entrapment risks around pools and hot tubs.  Anti-entrapment compliance is an ongoing responsibility and requires that staff are knowledgeable and aware of potential hazardous conditions.  If you have any questions or require documentation for your device please contact our office.  See below for some guidelines on testing common SVRS equipment, consult your owner’s manual for full instructions before carrying out any testing.

Vacless SVRS Testing

The Vacless requires monthly testing.  To test, leave main drain suction line valve(s) open 100% and close or plug off all other pool outlets on the pump suction lines.

Simulate entrapment by closing the main drain suction valve(s) that are installed within 2’ upstream of the pump.  The Vacless valve seal (piston) should activate (open).  This allows air to rapidly fill the pump and will cause a loss of prime.  Once activation is confirmed, open the main drain suction valve(s) and the valve seal should close and normal pump operation should resume.  Repeat this test three times, if the device does not perform as described above the pool is to be closed to bathers and additional troubleshooting will be required.

Stingl SR-500 SVRS Testing

The Stingl SR-500 requires testing anytime the settings are changes and recommends monthly testing.  Proper operation of the SR-500 must be verified by restricting flow to the pump while running in any of the normal operating modes (timed, continuous, and remote). Begin testing by covering the main drain sump(s) with a rubber mat. This will cause the pump to pull through the skimmer line(s) only, resulting in a higher operating vacuum. It may be possible to cover the drain and not increase the operating vacuum past the cut-off threshold. In these cases it will be necessary to close the skimmer valve(s) to create the vacuum necessary to create an alarm condition. NOTE: Repeat this test 3 times to verify proper installation.

PSP20 Automatic Shut Off Testing

The PSP Automatic Shut Off device requires testing every time the filters are backwashed or every 7-days to ensure the correct operation and programming of the H2flow Inc. PSP20. Testing consists of closing the pump suction valve causing the pump to dry run. The PSP20 should shut the pump down within 1 second.

On Pool applications with skimmer’s, close the skimmer valves prior to completing this procedure.

Ensure that the Timer has disappeared from The Display

To test the PSP20 for a blocked suction condition, ensure that the LCD display shows window 01

Close the pump suction valve. W ithin 1.0 Second the pump should shut down

The display will show Function Underload

The panel Reset push button Light will be illuminated, showing a blocked suction condition has occurred.

To reset the alarm and to restart the pump, press either the ‘Reset’ or the remote ‘RESET’ push button located on the door of the PSP20

Hayward Stratum SVRS Testing

The Hayward Stratum VR500 performs a complete internal system test during every start-up sequence.  Should anything change with the system design (plumbing changes and/or pump replacement), a test consisting of three simulated entrapments must be conducted to verify proper installation, calibration and operation.

An entrapment can be simulated by partially closing or repositioning a valve, so, that there will be a change in the flow pattern. That is, changing the pattern of flow from the suction outlet (Main Drain) to the skimmer will simulate an entrapment.

Field testing criteria to verify the release of a potentially entrapped bather is three simulated entrapments, in which the VR1000 turns off the pump and vents the suction line within three seconds in each of the three simulations.

Field testing criteria to verify the functioning of the pinched tube function is required. This function determines if the system can determine if the pump is connected to the VR1000 vacuum tube, when the pump is running.

A ball, butterfly or sliding gate valve shall be installed within 2 ft (0.6m) upstream from the STRATUM™ (between the STRATUM™ saddle for the vacuum tube and the protected suction outlet), or a test mat shall be used to cover the suction outlet to simulate an entrapment event.



Equalizer Lines & Anti Entrapment

If we were to discuss major operational changes over the last 10 years in aquatics, it would be hard to think of anything more prominent than anti-entrapment compliance.  As of Dec 2007, the United States federal Virginia Graeme Baker Pool & Spa Safety Act catapulted anti-entrapment risk management to the attention of aquatic operators and health inspectors across North America.  The AB pool standards have been heavily influenced by this American policy change.  When we talk about anti-entrapment, main drains on the pool floor immediately come to mind.  However, anti-entrapment refers to all submerged suction fittings.  This includes vacuum ports and equalizer lines.

Almost all pool fittings sold in Canada are designed and/or manufactured in the United States, it’s very difficult to find any suction fittings on the market that are not compliant.  The reality is most pool main drains in Alberta at this point in time are in compliance, sometimes the compliance can be difficult to assess (we’ve developed the Anti-Entrapment Evaluator™ report to help with this) but as time goes on and our awareness improves we are finding unique situations that are not compliant with the current standards.   Suction lines for jet pumps and feature pumps are often forgot about since there is typically no flow meter present on these systems, the false assumption is that the flow rate on the filter flow meter is telling us everything we need to know.  Another area of trouble is with equalizer lines.  If your pool system has wall mounted skimmer fixtures, there is an equalizer port inside (figure 1).  Manufacturers recommend the rear port is connected to the filter pump suction line and the front port (closest to the pool basin) is connected to a wall fitting approximately 1’ below the skimmer mouth.  If your skimmer has a functioning float valve (under the basket – figure 2), a drop in water level causes the float valve to drop and create a seal that connects the pump suction port to the equalizer port which allows the pump to safely run without cavitation as long as the water level remains above the side wall equalizer fitting.  At this time, the equalizer fitting becomes a functioning submerged suction outlet complete with a risk of entrapment/enlargement.  Hair entanglement is the leading cause of pool entrapment – excessive velocity pulls a swimmers hair through the grate, causing it to swirl and become knotted on the other side. (WHO 2011, ASPE 2013).  Without a functioning float valve, there is no connection between the pump suction line and the equalizer wall fitting.  An open equalizer line disconnected from the pump still allows a marginal benefit from an equalization of the water level between the pool basin and skimmer, allowing the water level to drop just a small distance below the skimmer mouth before cavitation becomes an issue.equalizer01

It is becoming more common to see equalizer ports on the skimmer tied into the floor main drains which eliminates having additional submerged suction fittings.

When anti-entrapment first started gaining momentum as an issue, many manufacturers were quick to design and manufacture approved retro-fit suction covers which have no doubt lead to selling a lot more replacement pool fittings.  Retro fit equalizer covers are a little more recent on the market and there several to choose from, if you want to look at your options just call our office and let us know what kind of skimmer you have along with a picture of the existing equalizer wall fitting and/or cover that is currently installed.

One option to deal with compliance is to disable the line – as per the 2014 AB Pool Standards.  Technically you could argue the equalizer line is considered disabled if there is no functioning float valve present – without the float valve there can be no suction connection and therefore the equalizer line is no longer a submerged suction fitting.  The open line between the pool and skimmer allows chlorinated water in and out to prevent unwanted bacterial growth from occurring.  You will want to discuss this option with your health inspector as it may not be considered ‘permanently’ disabled.

The best option is to keep your float valve and equalizer line in place as it was originally designed to prevent pump cavitation.  More pools these days rely on automatic water level control systems to ensure the pool has enough water to function.  Should your level controller fail, the water level can drop below the skimmer opening after a couple days of heavy use.  Approved retro-fit equalizer covers are readily available to adapt to most configurations.

If for some reason there is no available retro-fit option you may have to consider plugging off the equalizer line.  For this to be done correctly, the pool water level needs to be lowered so the line can be completely drained and dried out.  A plug is required on both ends otherwise the end of the line will become a dead spot and an area of potential bacterial growth that can eventually contaminate the rest of the pool, we do recommend against this as some types of skimmers are more sensitive to the water level and symptoms of cavitation can be experienced from the turbulence of splashing at water levels that are just slightly below normal operating.

Just like with main drains on the pool floor, anti-entrapment compliance for equalizer lines is an ongoing responsibility.  The risk is not totally mitigated once approved covers are installed.  We strongly recommend that the designated operator communicate to all involved staff about the importance ongoing anti-entrapment assessment.  We all know how important it is to test the water before allowing bathers to use the pool, a good practice for safety and risk management is to also ensure your submerged suction fittings are present and in good working condition.  While entrapment & entanglement incidents are rare, most accidents are due to missing or damaged covers.equalizer adapt


  1. World Health Organization (2006) Guidelines for safe recreational water environments. Vol. 2. SWIMMING POOLS AND SIMILAR ENVIRONMENTS. Geneva, World Health Organization.
  2. American Society of Plumbing Engineers CEU 202 – Public Swimming Pools. August 2013