I’ll call them. I hope they know what I’m talking about, because I sure don’t.
This is a tutorial to help you understand the difference between pressure and flow. If you take away nothing else, remember this:
Hydraulic pumps DO NOT make pressure, they MAKE FLOW. Pressure is made when a flow of a liquid meets a resistance to the flow.
Go perform this experiment: Take a "drippy" faucet. Say it drips a drop once every 5 seconds. That is a flow rate. The pressure behind the faucet valve is say 60 pounds per square inch. But a tiny amount of the water is escaping from the imperfect seal and is coming out of the faucet even if it is a very small amount. Now put your thumb over the leaky faucet and see the pressure rise over time against your thumb to the point that the full 60 pounds per square inch is applied against your thumb. Most people will not be able to stop the water from leaking around your thumb after a period of time. So the flow rate out of the faucet is very low, but the pressure that the faucet can develop against the resistance of your thumb is still the system pressure.
So putting a restriction in your hydraulic line of a smaller size connector can slow down the flow rate, but not the ultimate pressure that can be developed.
How much is the ultimate pressure that can be developed in your hydraulic system? That depends on several factors, not the least of which is the setting of the relief valve, the strength of the construction of the hydraulic pump and to a small extent the resistance of the piping and hoses own resistance to the flow of the fluid.
In a typical open center hydraulic system like your tractor has, there is some resistance to the flow of the pump in just the piping, connections, and hoses themselves. This resistance to flow is turned into heat. This is why everything gets warm with just circulating the fluid around from the intake to the pump, thru the open valves, thru the pipes and hoses and back to the reservoir.
This tiny amount of resistance in the system causes the pressure in the system to rise slightly, Usually around 100 pounds per square inch or so. Now if we open one of those valves, lets say the lift cylinders of your front end loader, what happens? The fluid flow is diverted from flowing back to the reservoir into looking at the cap end of two cylinders. So now the pressure starts to rise rapidly, but is still way under the setting of the relief valve.
As the pressure rises rapidly against the cap end of the cylinder trying to push the piston forward, lets say the pistons start to move forward, This stabilizes the pressure as the flow of the pump starts to fill up the cylinders and the piston continues to extend and the loader rises into the air. Of course the pressure that develops depends a whole lot on what if anything is in the loader bucket at this point. If there is nothing in the loader bucket the pressure developed in the cylinder will be much lower than if the loader bucket if full of wet sand lets say.
But lets pretend the loader bucket is empty, and still moving up. The pressure developed will still be fairly low because the bucket and arms are moving easily. Now lets say the cylinder rods have reached their end of travel. But you continue keeping the control valve open. Now the pressure in the cylinders are rising rapidly, the flow rate is diminished because the cylinders are full, and something has to give. Any number of things "could" happen, but what usually thankfully happen is that the pressure rises to the point that the relief valve opens and allows the flow to divert back to the "tank". Another word for reservoir.
But what if the relief valve is set to high, or is "frozen" closed? Something has to "give". Here are some possible outcomes. The pump could "grenade". In other words it could explode as the materials it is made from give way. Or a hose could burst, or the seals of the cylinders could give out, or the valve could explode. Or the engine could stall because its cam is unable to turn to drive the pump.
Remember, pumps make flow, not pressure. Pressure rises when that flow meets a restriction. Hopefully we have made a little clearer the relationship between Flow rates, Pressure, and resistance to flow and how they work together to determine what happens in your system.
