OMS ques.VRO?

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gwg

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After investigating how this fuel/oil pump actually works, I'm wondering how it could actually vary the ratio? The fuel diaphragm has a direct physical connection to the oil diaphragm. So if these diaphragms are working in sync, driven by crankcase pulses, how could they ever change the ratio? If they are designed to feed eg. 50:1, and the crankcase pulse speed increases or decreases, so will the pumping of these diaphragms, in sync, for 50:1. More fuel to more oil, Less fuel to less oil, depending on the speed of the pulses. So I don't see how it will very the ratio at any rpm range.

Or am I incorrect on this?
 

racerone

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????-------Have you looked at one of these pumps. ?---Taken one apart ?
 

dingbat

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...
Each engine revolution moves the piston (dark green) incrementally to one side of the air motor chamber (tan) and compresses the large spring. When the piston (dark green) nears the end of its travel, a small spring unloads a poppet valve located in the middle of the piston assembly. The pressure (white area) on one side of the piston rushes into the vacuum side (tan area) as the large spring quickly pushes the piston back to its starting point.
As the throttle is advanced, the pressure pulse gets stronger because of the increased airflow through the crankcase. This back and forth motion of the air motor's piston (dark green) is what powers the fuel pump and the oil pump. At idle and low throttle settings, the weaker crankcase pulses cause shorter piston movements, which in turn, pump less oil with each cycle. As the throttle opening increases, the stronger crankcase pulses cause greater piston travel resulting in longer oil pump strokes. That means, more oil is delivered increasing the amount of lubricant in the fuel up to a 50:1 ratio.
 

Chris1956

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I understand that newer OMS pumps create a straight ratio of about 60::1. They do not vary the ratio, based upon RPM.
 

gwg

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So If the OMS is not varying the ratio throughout the rpm range, whatever the ratio is eg. 50:1 or 60:1, then there should be no advantage in performance over premixing 50:1 or 60:1, providing your accurate with your mixing. Only the convenience of not having to mix fuel.
 

ondarvr

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I don't think I've ever heard an OMS system runs at 60:1, I have heard the total overall usage can avergae 60:1 though. This would depend on how you use the motor.

The OMS system varies the ratio less than the older VRO did.
 

flyingscott

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VRO and OMS are the same system. The name was changed because the vro pumps were being blamed for every engine failure deserved or not. They do not pump oil at a fixed rate they vary the amount from idle to full throttle.
 

Chris1956

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Gwg, The advantages of oil injection are that you always get a fresh oil/gas mix, no matter when you filled up, a reduction in the math required to add the right amount of oil and the convenience of filling a reservoir, vs mixing. Also, oil injection never forgets to add oil, which is something humans do all the time.

My motor (with OMS), idles much better because the fuel mix is precise and fresh. If you can get a motor with the OMS system, I would recommend you try it.

BTW - OMS was more than a name change.
 

ondarvr

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There were quite a few changes between the VRO and OMS systems, many of them were for warning information in case of a problem.
 
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gwg

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ondarvr, flyingscott, Im wondering, seriously, if you could explain to me how the VRO OMS varies the ratio, when you have an air motor, creating strokes from crank case pulses, connected to both the oil pump, and the fuel pump physically. It moves both diaphragms simultaneously. The only thing that is changing, is the strength of the pulses, so both fuel and oil diaphragm pumps stroke faster or slower simultaneously. How could the mixture change? If the system was designed to mix 50:1 or 60:1 it should be the same through out the rpm range?
 

ondarvr

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I have no clue as to how exactly they do it, it never concernend me. But the oil pump portion could easily be designed to pump a higher ratio as the the pump sroke increase with RPM's. I don't mean the same amount for fuel flow, but a higher ratio compared to fuel. Even by just using a different strength spring the ratio could vary.
 

gwg

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The oil pump is directly connected to the fuel pump piston (orange) and diaphragm so they work in tandem. As with the fuel pump, oil (yellow) is drawn in through the inlet fitting and a check valve as the air motor starts its travel. On the return stroke, the oil pressurizes, exits directly into the fuel chamber (blue area), and is blended while enroute to the carbs

To simplify things just remember that the air motor converts the crankcase pulses to a back and forth motion. Directly connected to the air motor is the fuel pump and the oil pump. The travel of the air motor pumps the fuel and the oil together to the carburetors and the alarm system monitors the oil pressure counts. Just like manually premixing the oil and gas, the VRO (OMS) automatically does the same thing and sends that fuel mixture to the carburetors.

These are quotes directly from the article that is linked above by Vic.S http://continuouswave.com/whaler/reference/VRO.html

The information above and the cutaway picture in the link http://continuouswave.com/whaler/reference/VRO.html, leads me to believe that it wouldn't vary the mixture hardly at all or not at all.
 

ondarvr

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I'm not going to stress over exactly how they did it. I work with pumping equipment almost every day, it isn't hard to vary a ratio even if they use the same shaft to actuate the mechanism for each fluid. Change the chamber size, diaphragm design, diaphragm material or strength, pressure in the pump, valving, etc. These can all change the ratio over a range of shaft movement. Just because the first amount of shaft movement might be at 100:1 doesn't always mean that the amount of fluid being moved increases at the same ratio for each fluid in the pump, as the shaft moves further at higher RPM's the second half of the travel could be at 50:1

I have no idea if these are the right numbers, I just used them as an example.
 
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WernerF

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gwg, your question about the various mixing ratios isn't dumb at all!

Since the oil piston and the fuel piston execute the same stroke both fuel and oil is pumped more or less. So the mixing ratio is only dependent on the ratio of fuel and oil piston cross section area and as a first approximation the mixing ratio should be constant.

The air motor is designed in a way that the stroke length (more exactly the leftmost position) depends on the pressure/vacuum in the air motor chambers. This is archeived by actuating the poppet valve not directly but with the small spring. With more pressure/vacuum in the air motor the poppet valve needs more force to be opened. Because of that spring the air motor piston needs to travel more to the left side to generate that force for the poppet valve to open and the piston to return.

But how does the air motor stroke influence the mixing ratio? I think it's due to the small volumes the oil piston is pumping. Unlike with fuel the very first portion of the oil pump travel is lost for pumping. Maybe the oil check valve needs some reverse oil flow for closing. Maybe it's in the movement of the oil pistons's O-ring. Maybe there is some play between the oil piston and the motor stem. The result is that on small strokes even less oil is pumped referred to the stroke length.
On large strokes the piston area ratio mainly determines the mixing ratio, that is 1:50. The characteristic of the small spring determines how short the strokes will be at what pressure/rpm/throttle. So mixture at idle can be adjusted by selecting another spring.
 

gwg

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First of all thanks to everyone involved in this topic this is a great discussion!
WernerF Do you believe the OMS pump is variable across the throttle range?I guess I look at this as you stated in a first approximation sense in your first statement of your explanation. The last part " But how does the air motor stroke influence the ratio?" we are only speculating on how it actually varies the ratio if it does at all. None of us seem to know how it would do it?

Is their someone who would know exactly how this pump varies the ratio, or if it does at all? Or does it do just what Chris1956 said it does meter it at 60:1 (OMS) thus
Oil Metering system?
 

flyingscott

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I am going to need a list of all the differences between oms and vro. That said there is a spring between the two diaphrams they do not work together. Think of it as two pumps in one housing connected by a metering device the spring is a pressure valve in the device. When the oil pump is working it is always trying to overcome the spring but it cant pulses are not strong enough so it can only put in a little Lets say 80-1. Then you give it more gas the pulses increase it starts to overcome the spring but its not a linear change now you are at 70-1. More gas ratio changes but its not a linear change now you are getting more oil to the gas. Then you decide hey this great I really want to crank the bejeebers out of it. Well the pulses get stronger the spring says guys thats it I'm outta here and he lets all the oil through that he can. Once again this is not a linear curve that is that's why you don't get it you think its always the same ratio it's not.
 
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