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Oil piping check valve use, installation & prohibitions: this article describes the use of check valves in heating oil piping systems. We explain where some manufacturers recommend that check valves should be installed, what the check valve is accomplishing, and we point out that other heating equipment and oil burner or fuel unit manufacturers prohibit using a check valve at all. We include citations from key industry sources & building codes on the use of oil piping check valves including Suntec & Webster.
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Check valves are recommended for use with home heating oil (No 2 fuel oil) on the oil supply line (the suction line) just above the oil tank in some heating oil pumping & piping installations in order to keep oil in the pipeline and to make service of a foot valve in the oil tank a bit easier.
Check valves are also used on No. 6 fuel oil systems, but at the oil pump as drain-back problems are less troublesome with heavier grade fuel. - Pump School (2012)
Shown at left is an oil tank foot valve, a check valve used to help prevent the loss of prime in the oil suction line. This valve is installed at the end of the suction line in the heating oil tank.
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The use of check valves on heating oil piping return lines has been found on some heating systems to prevent a messy oil spill from the return line and to make service of the fuel unit easier (Webster 2014). Check valves are described for this use to steer oil piping installers away from installing a fusible link type OSV on the return oil line - a possible cause of a fire disaster discussed separately at OIL LINE SAFETY VALVES, OSVs.
Watch out: while some manufacturers' literature (Webster) describes where and why a check valve may be installed on a heating oil system pipeline, other equipment manufacturers (Suntec) and sources prohibit their use. The worry is an oil-entrapment problem between the fuel unit and the return pipe that, combined with thermal expansion, is reported to cause return oil line leaks or leaks at the fuel unit itself. We have also read a claim that at fuel unit shut down the check valve could "blow the pump seal" - an explanation by Suntec.
If two oil lines are used to supply an oil burner, (a supply and a return) install an oil safety valve or OSV or fusible link oil line shutoff valve only on the oil supply line at the oil pump on the oil burner. Do NOT install an automatic oil line shutoff on the return oil line between the oil burner and the oil tank.
If a protection against oil back-flow at the return line is a concern, and if the manufacturer permits, use a check valve instead. Check valves like this one permit oil to flow just in one direction. They do not close down in event of a fire. Installed on the oil return line a check valve permits oil to flow from the oil pump in one direction only: back to the oil tank.
The check valve on the oil return line, like the OSV on the oil supply line, prevents oil from spilling back out of the oil piping should the service technician need to disconnect the oil piping from the fuel unit - for example during fuel unit servicing or repairs, or during service of a backup oil pump on larger and commercial systems.
As Webster points out, check valves in the suction line between the oil tank and their SPM units assures that the oil line and pump are always full of oil, supporting fast oil burner starts.
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You will find this arrangement more likely on commercial and multiple-burner installations such as we illustrate in Webster's sketch, adapted and annotated at left. [7a] There the oil supply coming from the oil tank is marked in green, passing through an oil pump, a check valve (red) and on to three oil burners through three OSVs (blue).
The oil return line is marked in light brown; you will see a second check valve (red) on the return line.
Oil Line Check Valve Mistakes & Warnings
Watch out: do not install a check valve on the inlet of a 1-pipe oil system and do not install a check valve on the return line of a two pipe oil system (as we just described above) IF the oil burner or fuel unit manufacturer recommends against it. Example: R.W. Beckett, in describing the installation of their Cleancut Single Stage or 2-Stage Fuel Units (Part No. 21844 and 21941 respectively) warns:
When Do We Use or Not Use a Check Valve on Oil Line Piping?
One manufacturer, Webster, explains where & why to use check valves on an oil line, and oil piping texts (NYFD 2012) also refer to their use to keep an oil piping header full or to prevent siphonage, while other manufacturers, Beckett and Suntec, indicate that we don't use them (at least with a particular oil burner model, or according to citation of a poorly-worded NFPA 31-25 8.5 that is confusing itself). So do we install a check valve or not?
And weighing in, some heating equipment manufacturers say check valves are not necessary.
Suntec Advice on Avoiding Use of Check Valves on Oil Piping
Suntec continues to point out that the effects of thermal expansion are leaks at joints, fittings, pressure gauges, filters, and fuel unit seals. The thermal expansion problem is most-likely in single pipe oil systems, in dual-fuel heating systems during alternate fuel use, and where the ambient temperatures are higher than the fuel temperatures - something particularly likely when pumping heating oil from an underground oil storage tank or after a fresh fuel delivery in winter.
Really? OK so this is confusing, right? Field technicians are obligated to respect the advice of the experts at the equipment manufacturer - in this case Suntec. But the applicability and use of check valves on oil piping installations may also depend on the installation particulars; some of the literature appears to contradict itself most likely because the manufacturers are describing oil piping on different types of systems: residential, commercial, and multiple heater applications.
Really? Suntec recommends use of an oil line pressure relief valve rather than a check valve if there is a problem on a particular oil piping installation - advice that does not address service convenience when working on a fuel unit connected to lengthy oil return piping that may perhaps even run overhead in some buildings.
Here's the bottom line:
More Check Valve Oil Piping Warnings
Watch out: where multiple heating appliances are fed from a common supply and return oil piping loop, a check valve is installed on the return line at each oil burner. [7a]
Watch out: some fuel unit manufacturers whose oil pumps include an internal check valve (Webster SPM series for example) may advise against installing extra external check valves on the systems where their equipment is used.
Watch out: Oil Entrapment Safety Warning:
Webster's Service Technicians Manual describes a potentially dangerous oil entrapment problem as follows:
If installed in the return line the valve would be pressurized, not open, cause the shaft seal to rupture or blow out & result in a major oil leak.
Thanks to reader Rick Johnston for adding clarification.
In contrast, Webster's Vacuum Breaker (P/N 48598) can be used in the oil suction line as a check valve. - Webster [7a p. 129]
Oil Line Check Valve Brands, Sources, Manufacturers
Oil Line Check Valve Troubleshooting & Diagnosis
When diagnosing high or abnormal vacuums (over 15 inches) in the oil supply line ahead of the fuel unit, don't forget to consider a debris-clogged or stuck check valve. Conversely, abnormally low vacuum may indicate an air leak in the oil piping system.
If the oil supply appears blocked and there is oil in the tank, in addition to checking for a blocked oil line or a debris-clogged valve or a sticking check valve, double check each check valve to be sure that it has been installed in the right direction. OSVs and check valves should have an arrow embossed on the valve body indicating the intended direction of oil flow through the valve, or some products may be embossed with an "IN" and "OUT" indication.
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