How to Prolong the Life of Your Gas Chlorinator The purpose of a chlorinator is to meter and deliver a set feed rate of chlorine gas from a chlorine cylinder (Figure 1). To do this, gas chlorinators must be operated and maintained properly. Direct Cylinder Mounting A vacuum-operated gas chlorinator reduces the gas pressure from a chlorine cylinder to less than atmospheric pressure and transports the chlorine gas to the point of application. The easiest and safest way to make the connection from a gas cylinder to the chlorinator is by direct cylinder mounting. In direct mounting, the chlorinator inlet valve is attached directly to the cylinder calve by a positive metallic yoke connection that is sealed by a single lead gasket. This soft-lead gasket should be changed every time the chlorinator is disconnected. After the chlorinator is placed on the cylinder valve, the lead gasket connection must be secured. One common error is to over tighten the lead gasket connection, which can damage the yoke of the chlorinator and, as a result of distortion, cause a leak. It is necessary to tighten the connection only one half to three quarters of a turn after contact is made with the lead gasket. After the chlorinator is secured on the cylinder valve, the valve should be opened only one quarter of a turn so it can be quickly closed in an emergency. Household ammonia vapor, applied at the lead gasket seal, will indicate chlorine leaks. Chlorine gas in the presence of ammonia vapor produces a cigarette-like smoke, a visual indication of a chlorine leak. If a leak exists, first check that the packing on the chlorine cylinder valve is tight. Second, check the lead gasket; however, this connection is usually tight. CAUTION: If the stem of the chlorine cylinder valve is difficult to open, do not force it. Damage to this valve could cause a chlorine leak. If the valve is difficult to open, it is much CAPITAL CONTROLS better to return the cylinder to the chlorine supplier, eliminating the risk of a gas leak caused by a broken valve. It is the supplier’s responsibility to provide valves in good condition. Also, when the valve is open, the cylinder wrench should remain on the valve. This provides for a quick shut-off (one-quarter turn) of the chlorine source. A label should be provided beneath the cylinder wrench, but on top of the valve, showing the direction in which the valve should close. If such a label is not posted, this could cause a valve to be turned in the wrong direction, thus opening, rather than closing, the valve. All chlorine valves are fitted with right-hand threads. Figure 1 - Schematic of Direct Mounted Gas Chllorinator 100.9050.0 Interconnection Manifold Direct mounting is by far the safest and most convenient way to mount a chlorinator to a cylinder, but is it is not always possible. If several cylinders are used to provide chlorine, then an interconnection manifold is necessary. The following three items are needed to make an interconnection manifold: the chlorine gas manifold - made of seamless steel pipe with a chlorine valve for chlorinator mounting, • • • a flexible connector (from the rigid pipe manifold to the chlorine source) - made of cadmiumplated copper. This provides a flexible line between the manifold and the chlorine cylinder, an isolation valve - made of bronze and located between the flexible connector and the cylinder valve. If the gas is maintained in a dry condition from the gas cylinder to the chlorinator, very little, if any, corrosion will result. When a chlorine pressure connection is broken, chlorine is exposed to the moisture in the atmosphere. This allows some moisture to combine with the chlorine gas. If moist air collects in the manifold, acids are formed and corrosion will occur that may cause the manifold to fail. The purpose of the isolation valve is to isolate the manifold from atmospheric moisture. The isolation valve is merely a valve equipped with an adaptor that is connected directly to the chlorine gas cylinder. Before the connection is broken, the isolating valve is closed and the chlorine gas cylinder valve is closed. Therefore, when the connection is broken, only a very limited amount of moisture will be allowed to enter the system. When a new container is connected and the connection is replaced, the isolating valve and the chlorine gas cylinder valve can be reopened. The use of an isolating valve can easily double the life of a chlorine gas manifold. The Ejector: Heart of the Chlorinator To understand chlorinator operation, consider the ejector the heart of the system. The ejector contains a 100.9050.0 venturi nozzle that creates a vacuum. Water pressure is supplied to this nozzle by a pump, and the differential pressure across the nozzle creates a vacuum. The vacuum then moves through a check-valve assembly, usually part of the ejector body itself, then through tubing to a rate valve, which controls the rate of feed of the chlorine gas. The vacuum level is reduced across the rate valve to a lesser magnitude at the diaphragm assembly of the vacuum regulator. The diaphragm assembly is connected directly to the inlet valve of the vacuum regulator, which has gas under pressure on one side and a vacuum on the other. The vacuum on one side of the diaphragm is about 20 inches (508 mm) of water column. The other side of the diaphragm is open to atmospheric pressure. This differential pressure causes the diaphragm to open the chlorine inlet valve (which has chlorine gas pressure on one side of it), allowing the gas to move, under vacuum, from the chlorine source, past the diaphragm, thought the chlorine flowmeter, past the rate valve, through the tubing, past the checkvalve assembly, into the nozzle area, and then into the water at the point of application. See Figure 1. It is most important to realize that chlorine is being drawn from the chlorine cylinder to the water via the vacuum created in the ejector. If the ejector is not functioning, the chlorinator will not operate. The vast majority of problems that occur in chlorination equipment can be traced to the ejector. Measuring Water Pressure A good service tool is a pressure gauge located just before the water inlet of the ejector. This gives a measurement of the water pressure that is available to the ejector. Measuring water pressure downstream of the ejector is somewhat more difficult, because the chlorine solution is corrosive. Downstream pressure is that which exists at a given installation as back pressure. Back pressure can be defined as a combination of the static pressure against which the chlorine solution must be injected, plus the pressure due to friction losses in the solution line. Both of these pressure must be considered because insufficient sizing of the chlorine solution line can amount to a considerable increase in back pressure, which may reduce the differential pressure across the ejector to such a point that the chlorinator will not operate. Various tools supplied by chlorinator manufacturers measure back pressure. A temporary gauge can be installed if there is some doubt whether an adequate pressure differential exists. Check-Valve Assembly Assuming the pressure differential is proper and the water flow through the ejector is adequate, the check-valve assembly, which is usually part of the ejector, is an area of concern. The check-valve assembly prevents water from entering the vacuum regulator portion of the chlorinator. If chlorine solution is injected in the presence of any positive pressure when the water flow through the ejector is stopped, a vacuum will no longer exist in the ejector. A positive pressure, equal to the static head into which the chlorine solution is injected, will exist. This positive pressure will exist at the check-valve assembly. If there is no check-valve assembly, the water will be forced into the vacuum regulator portion of the chlorinator. Check valve failure. Failure of the check valve is usually indicated by some quantity of water in the chlorine gas metering tube. The check-valve may fail for a number of reasons, the most common of which is an accumulation of deposits on the seat of the check valve. This means that even though the check-valve closes, it is blocked and not completely sealed, allowing water to pass through to the vacuum regulator. The second most common failure, depending on how frequently the check valve is cycled, occurs when the check-valve seat material becomes distorted. This is most common on systems, such as a deep well, where the pressure against the ejector and the number of cycles during a day are fairly high. Most chlorinator manufacturers offer several check-valve arrangements, depending on the pressure that the ejector is subjected to when the chlorinator is shut off. Generally, as the pressure increases, the stiffness of the diaphragm and the hardness of the check-valve seat increase. The check-valve is usually identified by the manufacturer with a mark on the ejector body itself. Consult the chlorinator manufacturer to determine of the proper check-valve is installed. Removing Water From the Chlorinator If water pressure builds in the vacuum regulator, the diaphragm assembly will move in the opposite direction of the chlorine inlet valve, and water will be allowed to vent to the atmosphere in the same way as when excess gas pressure builds in the chlorinator. Depending on the capacity of the chlorinator, it may be a simple operation to remove the water. If only a small amount of water enters the chlorinator and the check-valve problem is remedied, the chlorinator can be restarted and the water will be drawn out with the chlorine gas. It may be difficult to remove the water from low capacity units (less than 10 PPD/4.5 kg/h) because the quantity of gas drawn through the chlorinator is very small. To safely remove the water from small capacity chlorinators, remove the vacuum regulator from the chlorine cylinder source and allow the chlorinator to pull in air rather than chlorine. This will allow the chlorinator dry out so it can be reinstalled on the chlorine cylinder source. Where the metering tube is small, the liquid can cause the metering ball to stick. When this happens, it may be necessary to disassemble the chlorine flowmeter and manually dry it before the chlorine is returned to operation. When the check-valve fails, it sometimes becomes so distorted that it blocks the passage of vacuum and it appears as though no vacuum is present. If the ejector is operating properly, suction exists at the vacuum port and gas will flow. The Chlorinator’s Vacuum Integrity The remainder of problems associated with chlorinator are related to vacuum integrity. The chlorinator must be vacuum-tight from the ejector or the vacuum regulator inlet valve for a flow of gas to exist. There are three significant situations that can occur if there is a break in vacuum. No indication appears on the flowmeter, even though vacuum is being created. This indicates a vacuum leak at the top of the meter tube or somewhere downstream toward the ejector from this point. If the leak occurs above the float, this indicates the O-rings on the rate valve stem are not sealing. If the gasket on the top of the meter tube is not sealing, it has probable been caused by someone grasping the vacuum regulator by the meter tube when changing cylinders, thus dislodging it from its sealed position. When confronted with this situation, check all vacuum tubing and connections, the rate valve O-rings, and the gasket on top of the flowmeter for vacuum leaks. O-rings are used in most chlorinator to provide a seal between two parts. In the case of the rate valve, the Orings slide as the rate valve is moved. Although chlorinators are constructed of materials designed to withstand the effects of chlorine gas, even the most substantial O-rings eventually become brittle, and can actually remove themselves in the constant adjustment of the gas flow. They may disintegrate and be fed out through the vacuum tubing. When this happens, there will be a loss of vacuum through the rate valve. (Most chlorinator manufacturers provide spare parts kits, including O-rings, with their chlorinators). A vacuum leak somewhere below the float in the metering tube. This can be caused by a leak at the bottom metering tube gasket. In this case, the flowmeter will indicate a flow, but the flow will be air, not chlorine gas. If any connection below the bottom metering tube gasket leaks, air will register as gas flow in the flowmeter. The ejector is located at the chlorine application point. In the past, it was common practice to mount the ejector and vacuum regulator inside a cabinet. But for safety and economy, the ejector should be located exactly where the chlorine is to be applied. This eliminates pumping the chlorine solution to the point of application, which may be several hundred feet. By placing the ejector at the point of application, a break in the vacuum tubing will cause the chlorinator to shut off immediately, stopping gas flow or damage from chlorine solution lead, With a cabinet mounted ejector, a broken solution line to the application point could allow corrosive chlorine solution to contaminate the area. There are other advantages to placing the ejector as close as possible to the point of application. For example, this arrangement eliminates the back pressure resulting from friction losses in very long solution lines. When the vacuum regulator portion of the chlorinator is mounted directly at the chlorine source, gas pressure lines and the accompanying problems are eliminated. The gas is conducted under vacuum to the point of application, minimizing the hazards of pressurized chlorine gas and solution piping. However, the most practical configurations of equipment are not always possible. If solution lines are unavoidable, they should be routed to an area where a break will not cause damage. Also, valves within a solution line should be of the onequarter turn, PVC variety because these will cause the fewest maintenance problems and produce the lowest friction loss. Reprinted from an article published in Opflow, a publication of the American Water Works Association, July 1991, by Jesse Wolf, Technical Services Manager, Capital Controls Company, Inc. 100.9050.0 Design improvements may be made without notice. Represented by: CAPITAL CONTROLS Severn Trent Services 3000 Advance Lane Colmar, PA 18915 Tel: 215-997-4000 • Fax: 215-997-4062 Web: www.severntrentservices.com E-mail: [email protected] UNITED KINGDOM • UNITED STATES • HONG KONG ITALY • MALAYSIA 04/05 100.9050.0 Copyright 2000 Severn Trent Services
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