Need to measure leak rate of a tube by pressurizing to 4.5 PSI and reading pressure after one minute. How do I calculate rate of loss?

You can convert pipe size to gallons per minute of flow by calculating the cross-sectional area of the pipe and making some reasonable assumptions about pipe volume and the rate of flow. Pipe sizing is measured by the internal diameter of the pipe, not the overall outside diameter. Once determined, the overall volume can be calculated. Pipe flow is described in gallons per minute. Shorter lengths of pipe will have a greater flow than a longer length of the same diameter. This is caused by internal resistance of the pipe itself. By the same reasoning a larger diameter pipe will have a greater flow or GPM than a smaller pipe at the same pressure or flow rate. Pressure is described as pounds per square inch. The square-inch measurement is determined by the area of the pipe. The pounds are the amount of force that is placed on the liquid to push it through the enclosed space.With that background, you can estimate the flow based on the pipe size.
Find the cross-section area of the pipe. Area is equal to pi times the radius squared or a = 3.14 x r2. A two-inch diameter pipe would have a cross-section area of 3.14 x 12 or 3.14 square inches.
Understand that water has a certain pressure associated with the height of that water. One pound of water pressure, or 1 PSI, is equal to 2.31 feet of elevation in height. In other words, a 1-inch column or pipe of water that is 2.31 feet high will have a pressure of 1 PSI. The overall height -- not volume -- of the pipe corresponds to the pressure. A 6-inch diameter pipe that is 2.31 feet high will only have 1 PSI.
Find the volume of the 2-inch diameter pipe in Step 1 that has a length of 10 feet. Ten feet is equal to 120 inches. Multiply 3.14 square inches, the cross sectional area, times the length. The volume of the pipe is equal to 376.8 cubic inches of volume.
Convert cubic inches into cubic feet. One cubic foot equals 1,728 cubic inches. Divide 376.8 cubic inches by 1,728 cubic inches per cubic foot and the answer is .218 cubic feet. This means that the 2-inch diameter pipe that is 10 feet long has an internal volume of .218 cubic feet.
Calculate the amount of water that can be contained in the section of pipe at any given time. One cubic foot of water is equal to 7.48 gallons. Multiply 7.48 gallons by .218 cubic feet and the amount of water in the pipe is equal to 1.63 gallons.
Find the GPM if the flow of water is one foot per second. Multiply the one-foot per second flow by 60 seconds per minute and the flow is now 60 feet per minute. In other words the water will flow through the 10-foot pipe six full volumes for every minute. Since the piping contains 1.63 gallons per 10 feet of pipe, multiply 1.63 by six and the final GPM is equal to 9.78 GPM of water flow from the 2-inch diameter pipe.

I assume this has an electric blower and probably electric fuel pump? Does it have a fuel filter somewhere in the system? I'd try to return the fuel pressure adj. screw to factory setting. I'm guessing screw in decreased flow rate and out increases flow rate. If fuel pressure is measured on the burner side, then increasing flow rate should increase pressure. It's intuitively backwards. What does customer service say? Usually, they are helpful. They need to know there's a customer problem.

It should be between 120 psi, and 150 psi , but shouldn't vary more than 10 % between cylinders

pressure loss is either a bad fuel pressure regulator on the fuel rail where the injectors are, or a bad check valve in the fuel pump in the tank. usually the latter.

A quick test is to turn the key to on and measure pressure. Should be 40 psi. Pump will hum for 5 seconds and shut off if engine is not running. (Safety step).

Pressure should drop very little for 5 minutes.
You can cycle the key off for 15 seconds or until you hear the relay click off. Then turn key back on to start pump for 5 seconds again to build pressure. This will help get it started for the day as it builds pressure that bled down over night.

Please rate, thanks.

The fuel pressure should be 40-47 psi.This is with the key on and engine not running.Should stay at least 40 for about 5 or 10 minutes.Hope this helps.Good luck.

The first stop is to measure the pressure with an external gauge. if the readings are the same, surgery is needed, I would look at the oil pressure relief valve for foreign particles.

It takes resistance to make pressure, and your decsription does not sound good. If the pressure is actually dropping, and you find no issues with the oil pump and pick up, you need to measure bearing clearances... Essentially, everywhere oil is pumped needs to be inspected...

check cooling coil(in door unit)if there ice buil up then feel air vent if no air mean your fin block aready need to clean / air vent ok meant there have a leak .you need r22 test gauge and hose,reamer,tube cutter and flaring kit. 1)check suction pressure(big tube at out door unit) remove 2 way cap and 3 way cap valve then connect blue hose at service port 3 way valve (port locate at left or right depent on manufacturer) you will get pressure about 40-45 psi(air cond is running) then use a allen key(hexagonal wrench) to close 2 way valve(small tube or gas discharge side) wait 1-2 minute then close 3 way valve (suction tube or big tube) IMMEDIATELY SHUT OFF AIRCOND AND PLUG OUT POWER CORD (you need 2 person one at in door unit and the other at out door unit). this method is to keep remaining gas inside the compresser.Then leak check ,open 2 way valve about 90 degree hold it for 10 minute then close it .MEASURE THE PRESSURE keeep it for 5-10 minute. If the pressure indicate not same during the first time measured it meant there have a leakage, for air cond 1- 5 year the leakage will happen at the copper tubing connection and improper flaring .Then U need to clean in door and out door unit ,used a spanner or wrench to losen the copper FLARE NUT at out door unit and in door unit( inside insulation) then use pvc tape to cover all copper pipe/tube hole to prevent dirt go inside tube/pipe. Then lift up out door unit and used coil cleanner ditergent wait 5 minute then flush with water. Remove indoor front panel then disconnect out door unit cable at front panel in door unit then lift up indoor unit to disangage the hook and pull out the indoor unit, then clean the cooling coil ,cover electrical part with plastic .last step u need to cut (used cooper cutter)the copper pipe/tube FLARE NUT connection low side(big tube) and high side(small tube) in door connection and out door connection .Then u need to remove the burr from cut edge using reamer make sure metal powder not goes in Then make a flare after inserting FLARE NUT onto the copper pipes Then U can install back the unit check the low side pressure if the pressure 55-67 psi no need to charge

One of the factors used to designate compressor power is motor horsepower. However, this isn't the best indicator. You really need to know the amount of air the compressor can deliver at a specific pressure. The rate at which a compressor can deliver a volume of air is noted in cubic feet per minute (cfm). Because atmospheric pressure plays a role in how fast air moves into the cylinder, cfm will vary with atmospheric pressure. It also varies with the temperature and humidity of the air. To set an even playing field, makers calculate standard cubic feet per minute (scfm) as cfm at sea level with 68 degrees F air at 36% relative humidity. Scfm ratings are given at a specific pressure–3.0 scfm at 90 psi, for example. If you reduce pressure, scfm goes up, and vice versa. You also may run across a rating called displacement cfm. This figure is the product of cylinder displacement and motor rpm. In comparison with scfm, it provides an index of compressor pump efficiency. The cfm and psi ratings are important because they indicate the tools that a particular compressor can drive. When choosing a compressor, make sure it can supply the amount of air and the pressure that your tools need.

One of the factors used to designate compressor power is motor horsepower. However, this isn't the best indicator. You really need to know the amount of air the compressor can deliver at a specific pressure. The rate at which a compressor can deliver a volume of air is noted in cubic feet per minute (cfm). Because atmospheric pressure plays a role in how fast air moves into the cylinder, cfm will vary with atmospheric pressure. It also varies with the temperature and humidity of the air. To set an even playing field, makers calculate standard cubic feet per minute (scfm) as cfm at sea level with 68 degrees F air at 36% relative humidity. Scfm ratings are given at a specific pressure–3.0 scfm at 90 psi, for example. If you reduce pressure, scfm goes up, and vice versa. You also may run across a rating called displacement cfm. This figure is the product of cylinder displacement and motor rpm. In comparison with scfm, it provides an index of compressor pump efficiency. The cfm and psi ratings are important because they indicate the tools that a particular compressor can drive. When choosing a compressor, make sure it can supply the amount of air and the pressure that your tools need.

the flow rate in litres per minute (or litres/hour) is a very important measure of the cleaning ability. DIY machines commonly have flow rates as low as 6 litres/min. Heavy-duty industrial units vary from 10 to 40 litres a minute.