I am planning a piston squirter system for a project with some friends and wanted to gain 1st hand experience with flow through a small orifice and the effects of oil viscosity and pressure on such a system. I'll begin by thanking the previous contributors (Jim Casey, Dick Linn, Woody, et. al.) for sharing their valuable findings which have been a great guide. My experiments were conducted to satisfy my own curiosity and address the following elementary questions.
1. What volume of oil will pass through a given orifice at a given pressure?
2. How far will a given diameter stream of oil actually squirt?
3. What is the velocity of the stream at a given pressure?
4. How does oil viscosity affect flow through a small orifice?
5. What magnitude pressure loss occurs as you move downstream in a system from the pressure source?
I realize that we already have a relative feel for the answers to most, if not all of these questions, but the desire here was to better quantify such answers.
The test rig was very simple - a pressure vessel filled with a given test fluid (oil), pressurized with air, having a pressure gauge on the outlet followed by a discharge orifice (see attached pictures). I tested only one orifice size - 0.040" dia (flare fitting cap with hole drilled in it) - since this size is frequently encountered in this thread and in most recent factory production piston squirter applications I'm aware of. Connections and piping were all 1/8" NPT. To examine pressure loss between the tank and discharge point, two different lengths of 3/16" OD copper tubing (0.113" ID) either 19" or 9.5" were inserted between the tank and the discharge. There is no right or wrong size tubing or length for such an experiment, as I'm sure the selected tubes are too large or long for some of you and too small or short for others. The results from these sizes will nevertheless be informative and the trends will translate to other similar situations. When the copper tubing was fitted in the system a 2nd pressure gauge was attached at the end of the tube just prior to the discharge orifice so a comparison could be made between the tank pressure and the pressure at the end of the tube just prior to the discharge orifice. In such cases the 2 pressure gauges, i.e., tank and end of line, always read identical prior to flow starting (orifice plugged with finger tip pressure), but once flow commenced the terminal gauge dropped instantly to a lower value as shown in the attached plots.
The following 2 test fluids were used.
1. Blend - 5W-20 motor oil and WD-40 blended to provide a viscosity of ~ 16 cP, to mimic a 50 wt oil at a temp of 212F (ballpark internal hog engine temp). 50 wt oil has viscosity in the range of 16-22 cSt @ 212F.
2. Amsoil - 4-Stroke 0W-40 having a room temperature viscosity of ~ 100 cP. This oil was chosen because it was on hand, and provides an oil about 5 times the viscosity of the Blend.
Tests were conducted by filling the pressure vessel with test fluid, pressurizing to the desired tank pressure (5-20 psi), noting the pressure at the 2nd gauge if the additional copper tubing restriction was employed, and measuring the fluid volume discharged over a given period of time. In all cases only a single orifice was tested. In reporting the results (qt/min), the single orifice result was multiplied by 3 to represent the flow that would occur if 2 piston squirters and a pinion restriction, all being 0.040" dia were employed and fed with an unlimited supply of oil at the stated pressure. Stream velocity was calculated from the flow assuming the discharge was a uniform 0.040" dia cylinder. To determine the stream length of the discharged fluid the orifice was oriented to create a vertical stream, the stream directed up a nearby tree trunk, and a measurement made to the highest oil-wetted area of the tree trunk (worked from low pressure to high so wet line continued to climb).
Results are provided graphically in the attached link along with photos of the test rig. Some highlights of the experimentation are generalized below.http://tinyurl.com/bvkp7b7
1. Relatively high flows (1-2 qt/min) occur when employing a 16 cP fluid at orifice pressures of 5-20 psi. Higher viscosity test fluid significantly reduces flow.
2. At low test pressure (5 psi), increasing oil viscosity significantly decreases oil stream length.
3. Significant pressure drops (60-90% loss) occur when a 3/16" copper tube is interposed between the pressure tank and exit orifice.
As one might surmise from the above, employing a straight 50 wt oil at ambient temp or below would reduce flow and increase pressure far beyond the data ranges presented above (very little oiling going on following a cold start with straight weight oil). At full operating temperature (oil viscosity of 15-20 cP) and an actual pressure of 10+ psi at the orifice, flow potential of the 3 orifices would likely exceed the pump capacity.
If there are any questions or clarifications required on any of the above information, please ask and I'll try my best to address them. Hope you find something useful in the above.