Watts 0061935 1/2 In Bronze Dual Check Valve Backflow Preventer with Intermediate Atmospheric Vent, Female Union Inlet and Outlet Connections

The Watts 0061935 is a dual check valve with an intermediate atmospheric vent, which is the standard arrangement for a residential or light commercial boiler makeup water line. It is rated for non-health hazard protection only, and it guards against both backpressure and backsiphonage. That covers a closed heating loop with ordinary treated water. If the system carries a health hazard, such as glycol or chemical treatment, this is the wrong device class and you need a reduced pressure zone assembly instead.

Both ends are 1/2 inch (15 mm) NPT female threads, and both are union connections. The union is the part that matters on a boiler feed: you can break the valve out for service without cutting pipe or unthreading the whole run. Inlet is a union female threaded connection, outlet is a union joint.

No shutoff valves on either end. The 0061935 is the backflow device only, so you supply the isolation. On a boiler makeup line most inspectors and most service techs want a ball valve upstream and downstream so the unit can be isolated; the unions on the valve let you pull it out once those are closed. A strainer is built in, so you do not need to add one ahead of it.

The 0061935 is a non-testable device. There are no test cocks and no field test procedure, so there is nothing for a certified tester to hook a gauge to. When it fails, the atmospheric vent port drips and you replace or rebuild the unit. If your jurisdiction or your facility requires an annually testable assembly on that connection, you need a testable device instead, not this one.

No. The 0061935 is not built for hot and harsh water service. Watts builds separate hot water versions of its dual check line for that duty, and this is not one of them. Use it on cold potable makeup water. The 250 F fluid rating is a survival ceiling, not permission to run it as a continuous hot water device.

175 psi maximum working pressure, and a fluid range of 33 to 250 degrees F (0.5 to 121 C). That is well inside what a hydronic boiler feed sees, and it is rated for continuous pressure, meaning it can sit under line pressure all the time rather than being limited to intermittent duty like a vacuum breaker. The 250 F ceiling is fluid temperature, not a hot water service rating.

The vent is the difference. A plain dual check has two spring loaded checks in series and nothing else. The 9D style adds an intermediate atmospheric vent between the two checks, so if the upstream check leaks and pressure drops on the supply, the middle chamber opens to air and dumps rather than letting boiler water siphon back into the potable line. It also means you have to pipe or locate the vent where a discharge will not damage anything. Most codes call for the vented version on a boiler makeup connection and accept the plain dual check on lower risk connections.

It is not UL classified in the US or Canada, so do not specify it on a fire protection connection. Fire sprinkler and standpipe backflow protection needs a UL listed or FM approved assembly, and this is a potable water makeup device rated for non-health hazard service.

It is an inline body, so it drops straight into the run without changing pipe direction, and there is no integral elbow. Orientation still matters because the atmospheric vent has to be able to discharge downward and be visible, so plan the location around the vent port rather than around the pipe.

Brass body with rubber discs and rubber seats, made in the United States. Brass is the normal body material for a potable makeup line and it handles a mechanical room without any coating; there is no polymer coating on this one. The rubber discs and seats are the wear parts, and they are what eventually let a worn unit weep at the vent.

Neither. No bypass and no meter provision on the 9D, and no hydrant connection or cap and tether. It is a plain inline device: 1/2 inch in, 1/2 inch out, checks and a vent in between. If you need to meter makeup water to track boiler losses, the meter goes elsewhere in the run.