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Oil Line Safety Valve (OSV) controls: this article explains how to open or shut the oil line safety valve used on oil fired heating equipment.
We illustrate how to determine if the valve is already open or shut and we explain which way to turn the valve control knob to open or close the OSV.
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Reader Question: Can you tell me what position the stem should be in to use the valve as a manual shutoff
— when the handle is turned to screw the stem IN the handle comes off as the stem goes into the valve body
— when the handle is turned to move the stem out of the body it reaches end of travel with ~1/4’ of stem exposed
— I want to shut the valve to change the filter feeding the furnace
- Thanks S.N.
Reply: Which Way do I Turn the Oil Line Valve to Open or Close it to Permit or Shut Off Oil Flow?
S.N. Our pair of photos just above at OPEN or SHUT POSITION of OSVs show how to tell if the OSV is open or shut. Details are below.
Fusible-link oil line valves such as the Fire-o-Matic valve work opposite from usual plumbing valves - that is, internally these oil line control and safety valves work backwards from what you'd expect and backwards from ordinary plumbing stop valves.
Watch out: if the control valve on a heating oil line is not a fusible-link safety valve such as the Fire-o-Matic™, it will probably be an ordinary plumbing stop valve that works as all plumbing valves: clockwise closes those valves and counter-clockwise opens them. Sometimes we find a common stop valve on the oil line at the oil tank and a fusible-link safety valve just at each oil burner.
Details About Fusible Link Oil Line Valve Turning Directions to Open & Close the Valve & How the Valve Works Internally
An internal spring pressure, combined with a fusible link in the valve stem are what shut the oil line valve in event of a fire. In this design, when the valve is open to permit heating oil to flow it is also under spring tension. Because the valve includes a fusible link, 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.
Oil Line Valve Turned fully CCW (left to right) to Open Position = oil can flow
As you turn the handle on the oil piping safety valve counter-clockwise you will feel increasing spring tension as you are opening the valve (lifting the stem out of the valve body) against the spring pressure.
Because of the use of "reverse" threads on the valve stem, when you turn the OSV knob counter-clockwise the underside of the control knob, remaining in contact with the surface of the valve body, causes the valve stem to move up (against pressure of the valve's internal spring) until the threaded stem protrudes fully through the knob and you cannot turn the knob any more. In my photo the valve is about half-way open.
When the valve is fully open to permit fuel flow, the valve stem is "all the way out" of the valve body and the valve is being pushed-on by the internal spring. In this position the valve's knob has been turned clockwise, all the way down against the body of the valve.
When this oil line fusible-link valve is completely open to heating oil fuel flow, the valve stem is screwed all the way up "out" of the valve body. As you turn the valve knob clockwise you'll feel it moving against the internal valve spring pressure and you will see the valve stem moving up and out through the center of the oil valve knob.
Oil Line Valve Turned fully CW (right to left) to Closed Position = oil cannot flow
When the oil safety valve handle is screwed clockwise (right to left) so that the threaded rod has disappeared fully down into the valve body the valve handle will become loose and the valve internal components will be in the closed position - heating oil fuel will not flow.
Because of the use of "reverse threads" on the valve stem, when you turn the OSV knob clockwise , as the knob itself remains in contact with the valve body, the spring-loaded valve stem will move down into the valve body, closing off the oil flow.
As you turn the oil valve knob clockwise you will see the valve stem move back into the valve body and you will feel the spring tension on the device lessen.
For the last few counter-clockwise turns on the valve stem/screw you should feel a complete release of tension of the spring mentioned just above and if you keep turning the valve knob counter-clockwise it will unscrew and come off. Don't panic if this happens. The threaded portion of the valve stem protrudes up through the valve body and you can simply screw the knob back on.
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.
Summary of Oil Line Control Valve Open & Closed Positions
Put another way: if you turn the oil line valve until the handle begins to come off, the valve is in the CLOSED position. You will see that at this point you have removed all tension against the valve's internal spring and the spring has pushed the valve shut or closed. The valve stem has moved into the valve body.
If you turn the valve against its spring tension the valve is in its OPEN position. You will see that in this position you have turned the valve against its spring tension - the spring tension is increased - and the valve is open. The valve stem has moved out of the valve body.
We discuss using this valve for service to shut off the oil supply in our article on heating fuel oil filters found
Continue reading at OIL LINE SAFETY VALVES, OSVs or select a topic from the More Reading links shown below.
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OIL LINE SAFETY VALVE TURN DIRECTION to OPEN or SHUT at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.
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Frequently Asked Questions (FAQs)
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.
Question: What is the difference among all these different kinds of valves used on oil piping and at the oil burner or oil tank
What is the difference among all these different kinds of valves used on oil piping and at the oil burner or oil tank: check valve, fusible link valve, fire-o-matic type valve, vacuum operated valves, quickstop valves, solenoid valves, and oil delay valves. It's really confusing.
We agree that there are enough valves and enough similarity in their names that the controls used at oil tanks, on oil piping, and at the oil burner to manage the flow of oil can be confusing. Worse, valves that do different things and have different purposes may all be called "oil safety valves" in marketing and technical literature.
Don't confuse the built-in check valve in the fuel unit with external check valves, fusible link oil safety valves, solenoid operated quick-stop oil valves, and their sisters, solenoid operated oil delay valves.
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