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Vacuum gauge on oil supply piping (C) Daniel Friedman Heating Oil Piping Vacuum & Pressure Tests

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Oil line vacuum gauge & pressure gauge installation & testing:

this article explains the installation & use of heating oil piping vacuum gauges & pressure gauges to diagnose, test, & repair clogged or leaky fuel oil piping lines or filters.

How to install & use test gauges on oil piping. Where should the vacuum gauge be installed, how is it used, and what vacuum readings mean on the oil line. Where is a pressure gauge installed on oil piping and what are typical pressure or vacuum gauge readings on oil piping?



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VacuumTesting Oil Lines Detects Both Blockage & Leaks: Vacuum Standards for Oil Supply Piping

Vacuum gauge on oil supply piping (C) Daniel FriedmanReader Question: Is it normal practice to pressure test fuel lines when a new boiler has been fitted?

Is it normal practice to pressure test fuel lines when a new boiler has been fitted? We have an outdoor boiler that runs on a 2 pipe system as the storage tank is below the boiler.

The lines are buried as the distance between boiler & storage is 15-20 m.

We reported a vast increase in oil consumption after installation, would it be the normal course of action to then pressure test 'supply & return' lines? - Mark 5/29/12

Reply: How pressure & vacuum gauges are used on heating oil lines to check for leaks or fuel unit troubles

Mark, it is normal practice to inspect oil piping for leaks at all of its fittings & connections for leaks after a new installation, and there are indeed vacuum measurement tests (not pressure tests) that can be conducted that indicate an air leak into the oil supply line line (or oil leaks out when the fuel unit is not running).

But in my experience oil line vacuum tests are not performed as a matter of course but rather when a problem is under diagnosis, such as improper oil burner operation. And in my experience oil supply & return lines between the oil tank and the oil burner are not pressure tested. As I explain here, pressure testing those lines runs into some practical difficulties.

Similarly, a vacuum gauge installed on the heating oil supply line, often at or near the oil filter assembly, can help diagnose a leak in the supply piping itself.

Heating Oil Line Vacuum Reading Standards

Suntec gives this helpful guide to the use of a vacuum gauge and vacuum measurements on the heating oil suction line during oil burner operation - that is, while the system is running. This vacuum reading should be a routine check during heating system service, as it's diagnostic.

Table of Heating Oil Suction Line Vacuum Readings

Heating Oil Piping System

Maximum Running Vacuum Read

Comments

Single stage fuel unit, one-pipe system 6 inches of mercury (Hg) vacuum gauge  
Single stage fuel unit, two-pipe system 12 inches (Hg)  
Two-stage fuel unit, two pipe system 17 inches (Hg)  
Source: Heating Oil Pump Routine Maintenance, Suntec Pumps (2014)

Unfortunately in a two-pipe system we don't install and cannot as easily use a similar gauge on that second line to check for leaks.

In a two-pipe oil line system, the return line is never under vacuum, only under pressure when excess oil from the fuel unit is cycling back to the oil tank. Because the exit end of that pipe is open into the oil tank, it is not and cannot be "pressure tested" without some diassembly and the fitting of a plug at the line's outlet end.

Oil Supply Line Vacuum versus Oil Supply Line Pressure: What's the Difference? Where are They Measured?

Oil supply piping vacuum measurements

Oil supply piping vacuum measurements are made on the oil line between the oil storage tank and the fuel unit or oil pump that supplies high pressure oil to the oil burner. Increases in the vacuum level on the oil line can indicate oil line clogging.

Typically the oil line vacuum is measured by a vacuum gauge attached downstream of the oil filter - which also gives an indication of oil filter clogging - it's time to install a new oil filter.

Our photo above shows a vacuum gauge installedon a tee between the oil filters and the oil burner. Some installations include a stop valve between the tee nipple and the guage.

Leaving the stop valve closed when not reading the gauge reduces the risk of an oil leak at the guage itself - an improvement even more important if a guage is to be kept mounted on the oil supply pipe for pressure measurements as we discuss next.

Oil supply piping pressure measurements

Single line heating oil hook up (C) D FriedmanOil line pressure measurements are made at the oil burner by installing a pressure gauge in series on the high pressure oil supply line between the fuel unit outlet port or burner supply port and the oil burner nozzle - yellow arrow in our photo at left.

These pressure readings allow adjustment of the oil pressure supplied to the oil burner. Typical pressures range between 100 psi and 140 psi.

Many high speed oil burners currently operate at the higher pressure.

Note that because oil burner nozzle flow rates in gallons per hour (GPH) assume a supply pressure of 100 psi, when increasing the oil line pressure above the standard 100 psi it may be appropriate to change to a smaller nozzle orifice.

Oil burner nozzle companies provide a nozzle chart that helps in this selection.

See OIL BURNER FUEL UNIT for setting the fuel unit pressure in PSI.

Question: Is it normal practice to pressure test fuel lines when a new boiler has been fitted?

Is it normal practice to pressure test fuel lines when a new boiler has been fitted? We have an outdoor boiler that runs on a 2 pipe system as the storage tank is below the boiler. The lines are buried as the distance between boiler & storage is 15-20 m. We reported a vast increase in oil consumption after installation, would it be the normal course of action to then pressure test 'supply & return' lines? - Mark 5/29/12

Reply: How pressure & vacuum gauges are used on heating oil lines to check for leaks or fuel unit troubles

Mark, it is normal practice to inspect oil piping for leaks at all of its fittings & connections for leaks after a new installation, and there are indeed vacuum measurement tests (not pressure tests) that can be conducted that indicate an air leak into the oil supply line line (or oil leaks out when the fuel unit is not running).

But in my experience oil line vacuum tests are not performed as a matter of course but rather when a problem is under diagnosis, such as improper oil burner operation. And in my experience oil supply & return lines between the oil tank and the oil burner are not pressure tested. As I explain here, pressure testing those lines runs into some practical difficulties.

Similarly, a vacuum gauge installed on the heating oil supply line, often at or near the oil filter assembly, can help diagnose a leak in the supply piping itself.

Unfortunately in a two-pipe system we don't install and cannot use a similar gauge on that second line to check for leaks.

In a two-pipe oil line system, the return line is never under vacuum, only under pressure when excess oil from the fuel unit is cycling back to the oil tank. Because the exit end of that pipe is open into the oil tank, it is not and cannot be "pressure tested" without some diassembly and the fitting of a plug at the line's outlet end.

What causes pulsating oil pressure at the oil burner?

Reader question: Since I asked for one, my oil burner has a pressure gauge mounted on the unit showing the output pressure on the system. Usually the gauge is steady at 120 psi but now I see the needle is waving all over the place. What might be wrong. - anon

Reply:

I would be a little nervous about leaving a gauge on the outlet side of a fuel unit for heating oil equipment. There is a risk of blowout of the gauge and a horrible oil leak mess. That said, look for:

Other leaks and problems besides those air leaks above can also lead to oil burner shut-down or improper oil burner nozzle cutoff problems, including:

Incidentally, Suntec also offers these additional diagnostic suggestions regarding heating oil pressures: [8]

If oil pressure at the outlet side of the fuel unit is low, check the accuracy of the pressure gauge, then check that the nozzle capacity is not greater than the capability of the fuel unit. We add: check that someone has not misadjusted the fuel unit pressure screw.

Improper oil burner nozzle cut-off diagnosis - here is a diagnostic procedure from Suntec:[8]

With a pressure reading gauge in the nozzle port of the fuel unit (that is the fuel unit's output side), watch for a minute to see what happens to oil pressure as the oil burner stops running.

 

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