peebee
Out of Control
A "PRV" is a safety protection device. It is not a precision control device! If you want to use a PRV for something it wasn't designed for you must expect disappointments.
Below about 7PSI you are best relying on the wide surface area of diaphragms to get any accuracy, not springs and poppets (balls).
For gas-in, you can get variable LPG regulators in the 20-300mbar range (I use them) ... 300mbar is about 4½PSI. Some cheap small diaphragm regulators will hold down to 5PSI (most won't, often failing at 10PSI!). Small diaphragm regulators will "relieve" (control overpressure in the target) but require the backpressure of gas-in to be consistent (even though it doesn't use gas-in). Even diaphragm PRVs with no backpressure available have trouble maintaining pressure reasonably accurately compared to regulators acting "back-to-front". LPG regulators do not relieve (used for explosive gas!), so accurate very low pressure "PRVs" are difficult to find (and very expensive!).
Cheap pressure gauges are notoriously inaccurate, especially at low pressures. One source of relatively cheap low-pressure gauges that's been suggested to me are replacements for "blood pressure apparatus", but I haven't tried them yet.
That's taken quite a few of my years for me to figure out. Most people seem to believe the B.S. the manufacturers tell them (or don't tell them more like) ... or else make the B.S. up themselves!
Below about 7PSI you are best relying on the wide surface area of diaphragms to get any accuracy, not springs and poppets (balls).
For gas-in, you can get variable LPG regulators in the 20-300mbar range (I use them) ... 300mbar is about 4½PSI. Some cheap small diaphragm regulators will hold down to 5PSI (most won't, often failing at 10PSI!). Small diaphragm regulators will "relieve" (control overpressure in the target) but require the backpressure of gas-in to be consistent (even though it doesn't use gas-in). Even diaphragm PRVs with no backpressure available have trouble maintaining pressure reasonably accurately compared to regulators acting "back-to-front". LPG regulators do not relieve (used for explosive gas!), so accurate very low pressure "PRVs" are difficult to find (and very expensive!).
Cheap pressure gauges are notoriously inaccurate, especially at low pressures. One source of relatively cheap low-pressure gauges that's been suggested to me are replacements for "blood pressure apparatus", but I haven't tried them yet.
That's taken quite a few of my years for me to figure out. Most people seem to believe the B.S. the manufacturers tell them (or don't tell them more like) ... or else make the B.S. up themselves!
