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AFUE DEFINITION, RATINGS
AGE of CHIMNEYS & FIREPLACES
AGE of AIR CONDITIONERS & HEAT PUMPS
AGE of HEATERS, BOILERS, FURNACES
AIR FILTERS for HVAC SYSTEMS
AIR HANDLER / BLOWER UNITS
AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE
ANTIFREEZE for BOILERS
BACKDRAFTING HEATING EQUIPMENT
BACKFLOW PREVENTER VALVE, HEATING SYS
BACKFLOW PREVENTER, HEATER WATER FEEDER
BACKUP HEAT for HEAT PUMPS
BANGING HEATING PIPES RADIATORS
BLOWER FAN OPERATION & TESTING
BOOKSTORE - InspectAPedia
CAPACITORS for HARD STARTING MOTORS
COOL OFF HEAT, Thermostat Switch
COMBUSTION GASES & PARTICLE HAZARDS
DEFINITION of Heating & Cooling Terms
DIAGNOSTIC GUIDES A/C / HEAT PUMP
DIAGNOSE & FIX HEATING PROBLEMS-BOILER
DIAGNOSE & FIX HEATING PROBLEMS-FURNACE
DIRECT VENTS / SIDE WALL VENTS
DIRECTORY of OIL TANK EXPERTS
DRAFT MEASUREMENT, CHIMNEYS & FLUES
DRAFT REGULATORS, DAMPERS, BOOSTERS
DUCT SYSTEM & DUCT DEFECTS
FAN, AIR HANDLER BLOWER UNIT
FAN LIMIT SWITCH
FILTERS, AIR for HVAC SYSTEMS
FILTERS, OIL on HEATING EQUIPMENT
FIRE SAFETY CONTROLS
FLOODED HEATING EQUIPMENT REPAIR
FREEZE-PROOF A BUILDING
FUEL OIL TYPES & CHARACTERISTICS
FUEL UNIT, HEATING OIL PUMPS
GAUGES ON HEATING EQUIPMENT
HEAT LOSS INDICATORS
HEATING COST SAVINGS METHODS
HEATING LOSS DIAGNOSIS-BOILERS
HEATING LOSS DIAGNOSIS-FURNACES
HEATING OIL CLOUD WAX GEL POINT
HEATING OIL EXPOSURE HAZARDS, LIMITS
HEATING OIL - OLD, USEABLE?
HEATING OIL SHELF LIFE
HEATING OIL SLUDGE
HEATING OIL TANKS
HEATING OIL TYPES & PROPERTIES
HEATING OIL USAGE RATE
HEATING SYSTEM INSPECT DIAGNOSE REPAIR
HEATING SYSTEM NOISES
HEATING SYSTEM SERVICE FAQs
HEATING SYSTEM TYPES
HOT WATER HEATERS
LOW VOLTAGE BUILDING WIRING
MANUALS & PARTS GUIDES - HVAC
MIXING / ANTI-SCALD VALVES
MOTOR OVERLOAD RESET SWITCH
NO HEAT - BOILER
NO HEAT - FURNACE
NOISE, HEATING SYSTEMS
NOISE, WATER HEATER
ODORS & SMELLS DIAGNOSIS & CURE
ODORS FROM HEATING SYSTEMS
OIL BURNER FUEL UNIT
OIL BURNER INSPECTION & REPAIR
OIL BURNER NOISE SMOKE ODORS
OIL BURNER NOZZLE & ELECTRODES
OIL BURNERS, RETENTION HEAD
OIL BURNER SOOT & PUFFBACKS
OIL FILTERS on HEATING EQUIPMENT
OIL FILTER MISSING
OIL FUEL TYPES & CHARACTERISTICS
OIL HEAT FIRE SAFETY CONTROLS
OIL LINE CLOGGING FIX
OIL LINE QUICK STOP VALVES
OIL LINE SAFETY VALVES
OIL FILL PIPE LEAKS
OIL PUMP FUEL UNIT
OIL SPILL CLEANUP / PREVENTION
OIL TANK GAUGES
OIL TANK LEAKS & SMELLS
OIL TANK PIPING & PIPING DEFECTS
OIL TANK WATER REMOVAL
RELIEF VALVES - TP Valves on Boilers
RELIEF VALVES - STEAM TP VALVES
RELIEF VALVES - Water Heaters
RELIEF VALVES - Water Tanks
Reset Switch - Heater Primary Control
Reset Switch Broken - Quick RepaiR
RESET SWITCH - ELECTRIC MOTOR
Reset Switch - Stack Relays
SAFETY, HEATING INSPECTION
SAFETY RECALLS CHIMNEYS VENTS HEATERS
SOOT on OIL FIRED HEATING EQUIPMENT
STACK RELAY SWITCHES
STAIN DIAGNOSIS on BUILDING INTERIORS
STEAM HEATING SYSTEMS
THERMAL TRACKING & HEAT LOSS
THERMOSTATS, HEATING / COOLING
THERMOSTATS, WATER HEATER
VIDEO GUIDES: Heating System Videos
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Guide to OSVs - Oil Line Safety Valves: this article describes check valves and fusible link oil safety valves used on oil piping at heating appliances as both a fire safety device and to assist in oil burner servicing. We explain the purpose of OSVs, which way to turn the OSV or oil line safety valve to open or close it, and we describe common oil line valve installation or use mistakes. We describe and explain the differences in function and use among fusible link fire safety valves (OSVs), vacuum operated OSVs and PRVs, oil line check valves, Tiger Loop and other oil system air removing devices, and oil delay valves or quick-stop valves that are also referred to as oil safety valves. We explain where each valve is installed and what it does. We include oil safety valve and check valve troubleshooting advice, and we describe defects in heating oil piping & control valves.
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What are Fusible-Link Oil Safety Valves (OSVs) - definition
The OSV or oil safety valve controls flow of fuel oil to the oil burner of oil-fired heating boilers, furnaces, and water heaters. This inline oil valve is intended to close automatically and thus stop the flow of oil in the oil line in the event of a fire.
When the oil safety valve is open to permit heating oil to flow its movable stem and thus its internal stop valve are under spring tension.
Because the valve includes a fusible link (a lead or other soft metal core), in event of a fire the fusible link melts and the internal spring pushes the valve stem down, closing the valve and stopping oil flow.
Closing the oil valve means that we stop feeding oil to the oil burner in the event of a fire in the area.
This article series explains the installation & use of Fusible Link Oil Safety Valves (immediately below), Vacuum-Activated Oil Safety Valves, OSVs & PRVs, Check Valves on Heating Oil Lines, and Tigerloop™ or similar oil line de-aerator/prime-protection devices. Oil delay valves, also called quick-stop valves and also referred to as oil safety valves, are discussed separately at OIL LINE QUICK STOP VALVES.
Usually the OSV is installed close to the oil burner both for safety reasons (close to heating equipment means close to a more likely fire source) and also for service convenience. In our photo you can see from left to right the OSV (red arrow), an oil filter, and the fuel unit and air intake for the oil burner. That vertical pipe below the fuel unit is the return line - so we know this is a two-pipe or two line heating oil set-up.
Sometimes additional stop valves or OSVs may be installed at other locations (such as at the outlet of an above ground oil storage tank, but the critical location is at the oil burner.
The Firematic™ fusible-link automatic oil line shutoff valve (photo at left) should only be present on the oil supply line. We explain below that installing an OSV on the return line of a two pipe oil system can lead to disasater. Instead we can install a simple one-way check valve on the oil return line.
Our photo at below left shows an example of a Firematic™ safety valve right at the oil burner. Synonyms people use for this valve include OSV, fire safety valve, oil line valve, Fire-o-Matic valve, Fusible link valve, oil line shutoff valve, oil safety valve, and Fireamatic valve.
The standard oil safety valve used at the oil burner and often found also at the oil tank is the Firematic™ fusible link safety valve. The Firematic™ oil line valve can be installed in ANY position - (vertical, horizontal, upside down) at least that's what we were taught and what we have seen - the valve is spring loaded. In a fire a lead core melts at 165 degF and a spring in the valve assembly snaps the valve shut to assure that the heating system does not feed oil to a building fire. It has to work in any orientation.
At least three companies produce fusible-link inline oil safety valves (OSVs): ISP Automation (Firematic) , Asco Products (Emerson Industrial) , and a vacuum-activated OSV from Webster Fuel Pumps & Valves .
In our OSV photos below, the first photo (below left) shows the oil line safety valve in the OPEN positin - oil will flow when the threaded portion of the valve shaft extends fully up through the rotatable knob pointed to by my pencil. [Click any image to see an enlarged version. Thanks to reader Bernie Daraz for pointing out the need for these two photos]
In our heating oil line valve photo at above right the valve has been manually CLOSED - no oil will flow. The threaded valve stem has disappeared down into the valve body and has shut off the valve and oil flow.
Watch out: if (for example in case of a fire) the fusible link inside of an OSV has melted permitting the spring to close the valve, then from outside the valve may look as if it is in the open position - the threaded stem will still be poking out - but the valve has snapped and closed internally. Most likelyl you'll know this also because there will have been a fire or other horrible event that melted the OSV fusible link.
Which Way do I Turn the Oil Line Valve to Open or Close it to Permit or Shut Off Oil Flow?
Other Oil Safety Valve SNAFUS & Warnings
Watch out: A simple oil line shutoff valve may not be a fusible-link safety valve. The simple shutoff valve might be any plumbing valve that can manually stop oil flow in the line, but it is not a safety device.
Make sure you've installed a fusible-link safety valve at each location where it's most needed - at each oil burner. Even when one of these valves is installed at the oil tank the proper place for this protection is on the fuel oil supply line
right at the burner as well. Why?
Suntec points out in their installation literature for fuel units (oil pumps for oil burners) that pressures over 10 psi on an oil inlet line (normally running at a vacuum) may damage the shaft seal on the pump - i.e., leak heating oil.
SAFETY warning: If the oil line fire safety valves are missing or are not at the right location, we recommend immediate installation of a Fire-o-matic™ type oil line safety valve on the oil line at the burner.
Use a check valve instead. The automatic oil line shutoff valve should only be present on the oil supply line. Further explanation is below.
Our photo (left, red arrow) illustrates this hazard: you will see fusible link safety valves on both the oil feeder line (blue arrow, left side of photo before the oil filter canister) and the oil return line (red arrow, right side of the photograph).
SAFETY WARNING: If oil line valves are missing or are not at the right location there is risk of system malfunction, oil leaks, and fire damage.
We recommend installation of a Firematic™ fusible link (Fire-o-matic)™ type oil line safety valve on the oil line at the burner. This valve controls flow of fuel oil to the burner, and has a lead core which melts and shuts the valve, stopping the flow of oil in event of a fire in the building.
Even when a fusible link oil line valve is installed at the oil tank, the proper place for this protection is right at the burner as well. A valve in that location also makes servicing the heating equipment easier, faster, and cleaner.
Most residential heating equipment is supplied by oil piping that moves to from oil tank to oil burner by gravity (above ground oil storage tanks) and that is under negative pressure (a vacuum) when the oil burner is running: the oil burner fuel unit is pulling oil from the tank to the burner. Typically a spring-loaded fusible-link oil safety valve such as the Fireomatic type is used on those systems.
Vacuum-activated Webster OSV valves provide protection for pressurized oil line piping systems that may be found on central heating oil supply systems for multiple mobile homes, on commercial heating systems and at other installations in which a stand-alone heating oil supply pump is delivering oil to the equipment. Webster provides instructions for OSV use on both conventional gravity-fed oil fired heating equipment and pump-fed oil fired heating equipment.
Vacuum Operated Oil Safety Valves Protect Against Oil Spills
Webster's vacuum-activated OSVs provide protection against oil spills by preventing oil siphoning out of the oil tank should there be a break or leak in the oil piping between the oil tank and the oil burner(s). These valves are used with oil supply pump or booster pump systems and they also protect against excessive oil pressure at the oil burner inlet. Quoting Webster ,
Where to Install Vacuum Operated Oil Safety Valves OSVs
For vacuum-operated OSVs, unlike fusible link OSVs, an OSV device is installed not at the oil burner (since this is not a heat-activated fusible link device) but rather close to the oil tank, and an individual OSV and oil feed line is provided from the tank to each heating appliance. [Webster's sketch, above-left.] In the illustration shown above left (courtesy Webster Fuel Pumps & Valves .) the OSVs are at the oil tank and additional service shut-off valves are at the individual oil burners.
Watch out: Webster's instructions for OSVs include this warning:
Suntech's PRV Valves are OSVs that Prevent Oil Flow or Leaks When the Oil Burner is Not Running
The following description is adapted, parapthrased, and expanded from Suntec Industries information.
A PRV valve, such as Suntech Industries Inc.'s Model PRV-38 is an oil safety valve that prevents oil from flowing out of an oil tank by gravity, or by siphoning action, when flow is not desired. At the inlet side of the PRV valve, oil can be supplied under pressure or under a vacuum (depending on whether or not the oil burner fuel unit is running). But the PRV will not open to allow oil to flow unless it senses a vacuum.
This means that oil will not flow past this valve unless the oil burner and its fuel unit are operating. The effect is that this valve prevents oil from flowing out of an oil tank under any other conditions.
Why is a PRV valve installed? Suppose you have a large, above-ground oil storage tank at a facility, and that a leak occurs in the oil piping between the tank and the oil burner. Even if the oil line was cut entirely, the PRV valve will keep oil in the tank. In essence, the PRV valve is an oil leak and spill preventer.
PRV Installation & Use Recommendations
PRV Valves are installed as close to the oil tank as possible. And no, we don't usually find a PRV valve installed on residential heating systems. The PRV is mounted with its cap "down" if it's in an area exposed to moisture, to keep moisture out of the valve body. But it will work just fine in any orientation. Suntec's installation instructions for PRVs recommend that the valve be protected by a system filter.
If the PRV is used in a centralized oil supply system that is supplying fuel to multiple heating appliances, or if you are installilng the valve on a system that uses oil flow booster pumps, each oil burner should have its own PRV valve, as Suntec explains, to insure against high system pressures.
When installing a PRV or other valves and controls on oil fired heating equipment, do not use teflon tape. The worry is that a fragment of tape enters the system where it can clog a check valve or injure a device. Instead use a non-hardening pipe dope. We use a non-hardening version of blue LeakLok that works very well on oil fired equipment.
When you are priming an oil fired heating appliance, that is, bleeding air out of the lines, you can speed the process by pressing down on an exposed stem to hold the valve in an open position. We need this feature because the fuel unit does not pull such a strong vacuum on the oil line if the line is full of air (such as at a new installation).
PRV valves and No-Heat Calls
If there is an air leak in the piping system anywhere between the PRV valve and the oil burner, and if the air leak is big enough to prevent the burner from pulling enough vacuum to open the PRV, the PRV will remain shut, no oil will flow, and the burner will of course not operate.
You can test for this condition by pressing the prime button described above and checking for oil flow. A pressure gauge installed on the system can also be used to monitor for leaks (can the system hold a vacuum when the fuel unit shuts off?). We discuss pressure testing oil lines in the article above where we discuss Oil Safety Valves. You can also pressure test the oil lines under positive pressure.
If two oil lines are used to supply an oil burner, install a 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.
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 back to the oil tank. This makes service easier since we won't spill oil backwards out of the return line when working on the oil burner.
Check valves suitable for placement on the oil return line are available from various oil heat equipment producers including Webster.
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.
Watch out: Tigerloop™ warns that you should never install an oil line shutoff device between the de-aerator device and the oil pump.
Or as reader T.R. clarifies: ... I've been reading about TigerLoop oil fuel line de-aerators. When they are used, the manufacturer recommends that the fusible valve near the burner be attached at the inlet of their de-aeration device.
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Frequently Asked Questions (FAQs) about Fusible Link Oil Safety Valves (OSVs) on Heating Equipment
Question: Freeing up a stuck oil line control valve?
I think I have a valve that doesn't seem to turn off when fully turned counter clockwise. Any idea why? - P.C.
If you have a fusible link valve that doesn't seem to turn off you might try tapping the exposed end of the valve stem. I have found a stuck, or slow to close OSV on a few rare occasions. A gentle tap, not hard enough to damage threads, loosens it after which I open and close the valve a few times to convince myself it now moves freely. A burr on the brass interior or more likely internal sludge or debris could be the culprit.
Because at the oil burner the OSV is likely to be used at least once a year during service, that's a good opportunity to discover if the valve is not closing fully.
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