Oil line safty valve in the OPEN (oil flows) Position (C) 2013 Daniel FriedmanDefinitions of Types of Oil Piping Controls & Valves

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Oil Line Safety Valve (OSV) control types & definitions: this article illustrates & defines the different types of controls & valves used on heating oil piping systems, including check valve, fusible link valve, fire-o-matic type valve, vacuum operated valves, quickstop valves, solenoid valves, and oil delay valves.

We include links to details about the proper installation, use, & troubleshooting for each of these devices as well as manufacturers, brands, product sources.

Green links show where you are. © Copyright 2017, All Rights Reserved.

Definitions of Types of Heating Oil Line Control Valves

Oil delay valve required (C) D FriedmanQuestion: 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. - Anon 1/13/2012

[Click to enlarge any image]


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.

Here is a list of the different types of controls & valves used on heating oil piping, oil burners, and at oil tanks in order to assure proper and safe flow of heating oil to oil-fired heating equipment such as boilers, furnaces & water heaters.

Oil line valves, check valves, oil safety valves or fusible link valves (OSVs), and de-aerators or air removing devices are all defined. We include links to individual articles giving details for the installation, operation, and troubleshooting of each of these oil line controls.

Anti-Siphon Valves on Oil Lines

Anti siphon valve, EnvirosafeShown at left is an anti-siphon valve sold by Envirosafe, #710 Series Solenoid Valve (Normally Closed).

This anti-siphon valve is installed on the suction line exiting an above ground oil (or other liquid) storage tank to prevent accidental siphoning out of the tank should a leak occur in the piping downstream from the valve.

The valve is normally closed but will open when a dispenser pump is switched on. This product is provided by Envirosafe Above Ground Fuel Systems, 901 12th St., Clermont FL 34711, Tel: 800-555-4754, Website:, quoting:
Fuel Tank Check Valves:
Envirosafe™ Above-Ground Fuel Systems carries fuel tank check valves for above ground fuel tanks and other bulk fuel systems. We carry a variety of valves for bulk fuel tanks including vent valves, solenoid valves, by-pass valves, anti-siphon valves, and overfill prevention valves.

These [anti-siphon] valves are suitable for the dispensing of a variety of fuels including gas, oil, methanol, diesel, and alternative fuels.


Check Valves on Oil Lines: in-line check vales

Oil line check valve (C) Daniel Friedman

An in line oil piping check valve is a simple one-way valve installed on an oil line to prevent backflow or leakage.

Installers often place a check valve on the return line to the oil tank in two-pipe oil system.

Watch out: as we explain in our OIL LINE CHECK VALVES article, some equipment manufacturers prohibit the use of these check valves in their systems.

Details about the uses & prohibitions of check valves on heating oil piping systems are
at OIL LINE CHECK VALVES On Heating Oil Lines

Some oil piping safety and valve controls combine features and use confusing names. Webster's OSV is a vacuum-activated check valve that both protects against overpressure at the fuel pump and protects against spills in oil piping by preventing oil flow if a leak is large enough to prevent the oil burner fuel pump from drawing adequate vacuum in the line .


De-Aerators or Air Removing Devices for Heating Oil Piping & Lines

Tigerloop oil line foam and air remover (C) Tigerloop

De-aerators or prime protection fittings are special devices are available to protect heating oil piping and oil burners from loss of prime. The oil burner on an oil fired heating appliance can lose prime and thus stop working if there is air in the oil piping system.

Oil line de aerators operate by automatically removing un-wanted air from the oil piping system.

Air in the oil piping is likely to cause improper oil burner operation and can lead to loss of heat and also to dangerous

Details about oil piping de-aerators are
at TIGERLOOP™ or similar oil line de-aerator/prime-protection devices

Foot Valves in Oil Tanks

For some oil piping installations using No 2 home heating oil a foot valve may be installed at the suction line inlet in the oil tank; the foot valve acts much the same as a water well piping foot valve, keeping the oil piping system from losing prime by back-flow of oil out of the suction line into the oil tank when the fuel unit is not operating.

Fusible Link Oil Line Safety Valves - OSVs: fire protection device

Fusible link oil line valve (C) Daniel Friedman

Fusible link oil safety valves (OSVs) are installed in the oil piping to stop the flow of oil in event of a fire.

They are also a convenience for heating oil service technicians, allowing the service tech to turn off oil flow to change an oil filter or service the oil burner without creating an oil spill and a mess.

Details about OSVs are

valve operation details are at OIL LINE SAFETY VALVE TURN DIRECTION to OPEN or SHUT

Really? the term OSV or oil safety valve can be a bit confusing because in addition to the fusible link type valve described here - a fire safety device - some companies use the term OSV or oil safety valve to refer to vacuum-operated devices intended to prevent oil line overpressure or to detect and stop oil line leaks.

We describe vacuum-operated oil piping valves below in this article; and for details about them s

Oil Storage Tank Overfill Protection Valves

Oil tank overfill protection valve - Envirosafe The valve illustrated at left (better image wanted) is Envirosafe's 9095S Series AST (Above Ground Storage Tank) Overfill Prevention Valve.

This device, available from (800-555-4754), is described by the supplier as follows:

Designed for use on low profile tanks that require a high level shut-off. The valve terminates the fill when the product reaches the preset level. The valve can be retrofitted on existing tanks and fits into a 2″ opening.

A tight fill connection is required for operation. Sold with either a 2″ Part F Male Threaded Adaptor or a 2″ Part A Female Threaded Adaptor.

Typical flow rate is 53 GPM at 30 PSI. 

The company also provides a 9095A Series AST overfill prevention valve that is used i a "tight fill" application terminating flow into the tank when the tank reaches a pre-set warning level (90-95% full). The company notes that spill containers can be used for added spill protection around the oil tank.

Quick Stop & Oil Delay Valves at Oil Burners

Quick-stop valves and oil delay valves improve oil burner operation by eliminating the delivery of oil to the oil burner nozzle at low pressures.

Oil delay valve required (C) D Friedman

Details about quick-stop or oil delay valves are

Vacuum Operated Check Valves, OSVs, or PRV Valves Prevent Oil Flow When the Oil Burner is Not Running

Webster vacuum operated oil safety valve installation - Webster

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.

Really? These vacuum operated valves are called OSVs - a term used also for fusible link fire safety valves discussed above. But vacuum-operated OSVs are leak and oil line pressure protection devices, not fir safety devices.

What's the difference between a fusible link "firematic" OSV valve and a vacuum-operated OSV?

In short, while a fusible-link Fir-o-matic type OSV valve provides fire protection at the oil burner, a vacuum-operated OSV or PRV provides protection against oil leaks and for some applications it protects against excessive oil pressure at the fuel unit.

Details are at OIL LINE VACUUM-ACTIVATED OSVs & PRVs - live link given just below.


Continue reading at OIL LINE VACUUM-ACTIVATED OSVs & PRVs or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.


Suggested citation for this web page

OIL LINE CONTROLS & VALVES at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia


Frequently Asked Questions (FAQs)

Click to Show or Hide FAQs

Ask a Question or Search InspectApedia

Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.

Search the InspectApedia website

Comment Box is loading comments...

Technical Reviewers & References

Click to Show or Hide Citations & References

Publisher's Google+ Page by Daniel Friedman