It’s true, on the surface, but just because something is simple doesn’t mean that it’s good for you. “Metric is simple, because base-10 is simple, and therefore it’s better for everything,” is the doctrine I was taught. It’s useful to be able to think in ways other than base-10. Some number systems are base-5 or base-20, or base-2, or base-16. Some things are easier to think about as fractions, some work better as decimals. There’s lots of perfectly good boats and other technology out there that require you to speak their language.Īnd by the way, numbers /are/ a cultural-linguistic thing. All my old-timey mentor-type people prefer the old units. The ability to use both and convert between them is super useful. The good Captain from Maine, seemed happier with psi, so I used psi for my examples. Both I use both because I can interface with the world more effectively that way. But if I didn’t know exactly what 9/16" looks like, I’d be a crappy mechanic.
When will you guys learn how to use a simple system like the metric? Just because Ronald Reagan didn’t doesn’t mean it is rocket science. We might want the gauge to read relative to some number higher than atmospheric… But why wouldn’t you just use a differential pressure gauge? I don’t know why we have this, but we do. Let’s imagine that we are making a CO2 extinguisher to use in a hyperbaric chamber. Apparently it reads the pressure relative to some chosen fixed value. The fourth type of reading is called “Sealed pressure.” I’ve never seen this one used. If the inlet pressure on my pump is Absolute 14.5 psi, and the outlet pressure is absolute 24.5 psi, the differential gauge will show 10 psi. The third type of reading is “Differential pressure.” If you have a gauge in parallel with a pump or an orifice, it is measuring the difference between the inlet and outlet pressure. When my tank is 14.5 psi, then it’s about the same as atmosphere, and if it reads more than that, it is under pressure. The second type of reading is “Absolute pressure.” When this reading is zero, my tank is experiencing hard vacuum. If my gauge pressure is ‘zero’ it means that my tank is equal to the current atmosphere, not that it has a vacuum. If I have a pressurized tank, and a low pressure weather system moves in, the gauge pressure inside the tank will be higher, even though nothing inside the tank has changed. “Gauge pressure” is pressure relative to the current atmospheric pressure. It’s important to know that pressure is measured in different ways, which make certain readings not directly comparable to others. This gauge is in kPa, 10,000 kPa (10 mPa) *should be about 1450 psi. So on the fire main if the gauge reads *0.5 MPa that’s about 70 psi, *100 psi is going to be about 0.7 MPa etc. So if 1 bar (0.1 MPa) *is about atmospheric pressure *or 14.5 psi than: Pascal (Pa) is a whimpy European unit so it takes a lot to amount to anything, 100,000 Pa just to get to 1 bar, so 10 bar is *1,000,000 pascals or 1 MPa, which is the units the new gauge uses.Ītmospheric pressure is about 14.5 psi. I know atmospheric pressure at sea level is about 14.5 psi so that gives a number to use for rough conversions.īar it is is not an official SI unit but it is *based on the metric system so *bar can be converted exactly to the *pascal which is the official SI unit of pressure. Atmospheric pressure varies of course *but is about 1000 millibars or 1 bar. That had me scratching my head, *till I went to log the barometric pressure which is measured in millibars (mb). What the? * Looking it up *1 MPa = 10 bar. This gauge is in kPa, 10,000 kPa (10 MPa) should be about 1450 psi.Ī few years back *we got a new fire main pressure gauge in MPa. So on the fire main if the gauge reads 0.5 MPa that’s about 70 psi, 100 psi is going to be about 0.7 MPa etc. So if 1 bar (0.1 MPa) is about atmospheric pressure or 14.5 psi than: Pascal (Pa) is a whimpy European unit so it takes a lot to amount to anything, 100,000 Pa just to get to 1 bar, so 10 bar is 1,000,000 pascals or 1 MPa, which is the units the new gauge uses.Ītmospheric pressure is about 1000 millibars or 1 bar.(from the barometer)Ītmospheric pressure is about 14.5 psi. (about atmospheric pressure)īar is not an official SI unit but it is based on the metric system so bar can be converted exactly to the pascal which is the official SI unit of pressure. I know atmospheric pressure at sea level is about 14.5 psi so that gives a number to use for rough conversions.ġ000 mb = 1 bar. Atmospheric pressure varies of course but is about 1000 millibars or 1 bar. That had me scratching my head, till I went to log the barometric pressure which is measured in millibars (mb). A few years back we got a new fire main pressure gauge in MPa.