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I have two machines for testing solenoids, one new and one old.

When a bypass is connected to both hoses (the input hose is connected to the output hose), I get ~1:1 for the input output pressure; the input pressure gauge matches the output pressure gauge. I tested with roughly 85 PSI and for the input and I was getting 85 PSI for the output.

When using a solenoid block and solenoid (normally open solenoid, no power) the old unit still gives me an output pressure very close to the input. (There is a small loss because some fluid leaks out the top of the solenoid block; it's not perfectly sealed.)

Using the same solenoid and block, my new unit shows a much larger loss in pressure, roughly 10psi difference from input to output. (In this case 85PSI in and 75PSI out.)

There are differences between each unit. The new one has a larger motor for example. And while I expect some pressure loss, I can't explain the difference because both my inputs match, and do not change between each unit. Can something else inside the machine, explain this difference?

EDIT 1:

![new unit] (https://drive.google.com/file/d/1FYrI3dKGz2JRw69twLbEfXc1Kvgr7jED/preview)

old unit https://drive.google.com/file/d/15Cmr_BLh8bd_aMpLOZIYaC2AhPzcu34h/preview

Hopefully this helps, I have also flushed the system so there are no air pockets on the new unit. Could there be some kind of fluid dynamics happening in the hose that cause this on the new unit?

EDIT 2:

Clarification, the newer unit has a larger pump (I called it a motor). When I say strain gauge, I mean pressure transducer which gives me a live reading from the PC controlling the hardware. And yes, the solenoid block is essentially a metal block with two quick release couplings on the side. On the top of the block, is a hole fitted for solenoids to be quickly added/removed for testing purposes. There is flow but not power to the solenoid, which is normally open. The motor powers the input flow. From an operators perspective, there is simply an input hose and an output hose

The pictures show how I have the setups, I tested using the same solenoid block, and setup so ignore how they are setup in the photo. Is it possible the the size of the hose has some play into the pressure measurements?

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  • $\begingroup$ When you say you're testing solenoids do you mean that you are "testing solenoid-operated valves"? You should only be getting a pressure drop if there is a drop in pressure due to flow through a restriction. Is this a static test or is there flow? You mention "motor" but don't explain where this sits in the circuit. A fluid schematic would be helpful. $\endgroup$
    – Transistor
    Nov 30, 2023 at 19:22
  • $\begingroup$ I don't understand "strain gauge." Do you mean pressure gauge? Nor do I understand your layout. Can you diagram it? $\endgroup$
    – Tiger Guy
    Nov 30, 2023 at 19:39
  • $\begingroup$ yes when I say strain gauge, I mean pressure transducer which gives me a live reading from the PC controlling the hardware. And yes, the solenoid block is essentially a metal block with two quick release couplings on the side. On the top of the block, is a hole fitted for solenoids to be quickly added/removed for testing purposes. There is flow but not power to the solenoid, which is normally open. The motor powers the input flow. From an operators perspective, there is simply an input hose and an output hose. $\endgroup$ Nov 30, 2023 at 20:14
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    $\begingroup$ All that info belongs in the question rather than in the comments which can be deleted. Similarly your image links won't be any use when the links die. By "motor" I suspect you mean "pump". $\endgroup$
    – Transistor
    Nov 30, 2023 at 21:27
  • $\begingroup$ Measurement of pressure can get tricky when there is flow. Are you measuring static pressure with long tubes (diameter relative to main pipe matters in how flow affects) perpendicular to the wall of a larger pipe or is it picking up some of the dynamic pressure by being in the flow? $\endgroup$
    – Abel
    Dec 2, 2023 at 11:16

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