Oil quick stop valves or delay valves: this article describes solenoid operated quick stop valves used at oil burners. These oil safety valves, when they include a timer that delays valve opening at burner start-up, are also referred to as oil delay valves or oil delay solenoids.
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. Low pressure oil delivery, which can be caused by air leaks or just slow burner start-up, causes dirty oil burner operation and can lead to loss of heat or dangerous oil burner puffbacks.
Here we explain how and why quick stop and oil delay valves are used, how they are installed, and how to diagnose problems with OSVs and quickstop or delay valves.
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Oil heating technicians use at least four names for versions this device: an oil shut-off valve, an oil delay valve, a solenoid safety valve or a quick-stop valve. Some sources such as Sid Harvey also refer to this control as a "Magnetic Oil Burner Valve" (Honeywell).
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Except for the presence or absence of providing a valve opening delay at oil burner start-up, these are all the same type of product and they have the same basic purposes:
Shown in our photo above is R.W. Beckett's PD Timer part number 21887, a 120VAC 50/60 Hz control that provides a four second delay at burner start-up. The valve is rated for operating temperatures up to 150°F.
In standard installations the fuel oil pumping unit sends high pressure heating oil through its outlet tube to an inlet fitting on the oil burner that in turn sends that high pressure oil to the oil burner nozzle where it is sprayed and ignited in the combustion chamber. When the oil burner tops, we want to quickly stop the flow of oil to the nozzle.
If we don't stop the oil flow quickly, heating oil at lower pressure continues to squirt, then dribble, out of the end of the nozzle where it will not benefit from complete combustion.
The result is an accumulation of un-burned heating oil in the combustion chamber - the cause of a "bang" or worse an oil burner puffback at the start of a subsequent oil burner "on" cycle.
Oil burner fuel units (oil pumps) already contain an internal check valve intended to quickly stop the flow of oil to the burner when the oil burner motor stops. But with age, or more likely with the passage of dirt and sludge from the oil tank, through the oil lines, through the oil filter, and finally sneaking past the internal filter screen found inside the fuel unit, that crud, or some of it, lands on the internal check valve seat where it can cause the valve to fail to seal quickly or completely.
An oil delay solenoid switch or valve, also popularly referred to by some service techs as a quick-stop valve, is an electrically operated valve installed on the oil line between the fuel unit and the oil burner nozzle assembly.
Our photo (left) shows a new oil burner fuel unit installed on our older Beckett oil burner. It's worth reading the label on the fuel unit - it warns Use Only with Valve on Delay.
The oil delay valve, operated by an electrical solenoid switch, closes to immediately stop the flow of oil to the oil burner assembly the second that electrical power to the oil burner is shut off.
This quick-stop valve is a handy "fix" that we can add to an existing oil burner fuel unit if we think that its internal check valve is not working properly. (Few technicians would attempt to disassemble and clean the fuel unit to that level of detail, and an oil delay valve is less expensive than a whole new fuel unit.)
When the oil burner motor starts, the power circuit also powers the oil line solenoid valve. We call the device an oil-delay-valve because the valve includes a built-in time delay that allows the oil burner motor and blower assembly to spin for a brief time before the valve opens to permit oil to pass on to the burner nozzle. This delay, an added feature, helps establish draft and reduces sooting at the oil burner.
Interestingly, some fuel units now come from the manufacturer with an oil delay valve assembly already attached. The importance of a sharp clean cessation of oil flow makes this added feature desirable. We had asked our heating service company to install an oil delay valve on our oil burner to stop a startup "Bang" and soot problem that was chronic on our lab heating system.
Bob, Bottini's service tech, inspected more closely and found that the fuel unit had a small leak around its shaft. That leak sent oil into the oil burner assembly, crudding up the oil burner combustion air fan and adding to a dirty oil burner flame problem.
Since our oil burner fuel unit needed to be replaced anyway, it was more economical to install a new fuel unit that included as well an oil delay solenoid valve than it would have been to buy and install those parts separately.
Wiring the oil delay solenoid: for most models, the solenoid valve's electrical wires are connected to the oil burner "run" circuit inside the primary control by connecting the solenoid control circuit wires to the oil burner motor leads - in this case, the nearby cad cell relay.
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The standard oil burner solenoid valve cord set can be replaced with a PD timer kit such as the R.W. Beckett PD Timer #21887U that provides a precise 4-second delay between the oil burner motor start-up and the opening of a valve that admits oil from the fuel unit to the oil burner nozzle. You should follow the wiring diagram that will certainly come with the product that you purchase.
Above we provide an example wiring diagram for an oil delay valve time, from Beckett's 21887U PD Timer delay cord set.
To be clear, we want a zero-second delay at oil burner shut-down, as we explained above. But we may want our solenoid operated shut-off valve to delay its open by a few seconds to allow the burner and blower assembly to get up to full speed, improving draft and combustion air flow to assure a very clean start-up when oil is released to the oil burner nozzle and igniter.
Suntec, a manufacturer of fuel units and delay valves describes a solenoid dumping pump used on their A-7400 fuel unit as including
With a dumping solenoid incorporated in the charge circuit, [so that] nozzle cut-off occurs quickly, while the blower is at nearly full speed. The solenoid itself contains a thermistor which provides an approximate delay of 2 seconds on start-up, ensuring nozzle cut-on at high blower speeds.
Solenoid operated shut-off valves are sold in both non-delay models (Such as Suntec R642NL) and delay models that provide a 1-2 second delay (Suntec R641DL) or a 3-5 second delay (Suntec R643LL) or even up to 15 seconds of delay to suit various application needs.
On a recent no-heat call we were embarrassed to learn from Bob, the service tech, that the problem was most likely that somebody had accidentally knocked loose an electrical connector at the oil delay valve (aka "quick stop valve").
The valve in our photos is used by Beckett on some oil burner models (depending on fuel unit features) and is labeled PD Timer.
The connector may still appear to be in place but may have been pushed slightly back or askew.
The result is that on a call for heat the oil burner motor will run but the burner will never ignite.
Because the oil delay valve delays forever - without its own electrical connector it never opens. The result is that the burner will shut off on reset due to a failure of the cad cell to see flame.
We tied the rubber boot (black rectangle at the right side of the valve itself) to the PD Timer oil delay valve body (gray in center of the photo) using plastic ties.
As Bob pointed out, this step to prevent the oil delay valve or PD Timer connector from being knocked loose again is ok as long as you're not foolish enough to wrap the plastic tie around the oil line (copper in our photo, above the PD Timer delay valve body).
The PD Timer is produced by RW Beckett, a manufacturer of the oil burner in our photos indicates that an alternative to the PD Time is to "Use 21844U Clean Cut Pump without PD Timer when primary control has a pre-time (valve on delay)."
We might wish that the manufacturer of the PDTimer had included a simple clip that would prevent the connecting wiring boot from being knocked off of the valve body. Other than the loose-connector trouble leading to no-heat calls, this quick stop / oil delay valve has performed flawlessly on our test system since installation.
Don't confuse oil safety valves, oil delay valves, or oil quick stop valves discussed just above with
OIL LINE CHECK VALVES on Heating Oil Lines, and
Tigerloop™ or similar oil line de-aerator/prime-protection devices.
For help sorting out these controls see OIL LINE CONTROLS & VALVES.
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