My understanding is that the evap canister vent valve is normally open, allowing filtered air to vent to atmosphere. Then, when the vehicle is off for a couple hours, the PCM powers the solenoid (12V) to close it and runs a vacuum test.
The canister vent solenoid is normally open, and is closed only when the evap system is undergoing a leak check monitor. A vent valve that's stuck closed will cause refueling problems.
The vent valve is a device installed to prevent negative pressure (e.g. as a result of surge pressures) in a piping system. Vent valves are also installed at the highest points in a piping, system downstream of shut-off elements or pumps, and at the highest points in domestic installation systems.
In operation, the pressure relief valve remains normally closed until pressures upstream reaches the desired set pressure. The valve will crack open when the set pressure is reached, and continue to open further, allowing more flow as over pressure increases.
Generally speaking, the valves are basically clockwise to close valve and opened counterclockwise, or left open and right closed.
Mount PRVs in a vertical position, which means upright and with the spindle vertical. A valve installed in any position other than vertical might not perform correctly. For flanged valves, be sure to draw the bolts down evenly. This is especially crucial for cast iron valves.
Collapsed Fuel Tank
When the purge valve is stuck wide open and the vent valve is closed, an excessive vacuum is created within the EVAP system. Although rather uncommon, a purge valve that is stuck completely open can cause the fuel tank to collapse or deform.
The caps on auto vents should be left open. Only if vent starts to leak water, tighten cap closed then replace vent. Autovents release air as it accumulates.
A safety valve vents to prevent a predetermined safe pressure from being exceeded. Normally used with compressible fluids. A relief valve vents to prevent system pressure exceeding a predetermined pressure. Normally used with incompressible fluids.
The most universal cause of water hammer is a valve closure, in which fluid flow is rapidly decelerated causing a large increase in pressure. During a valve closure, the kinetic energy of a flowing fluid is converted into potential energy in the form of pressure.
If the valve is stuck open, your engine will not get a warm start because the exhaust will be channeled straight out the tailpipes, instead of around the base of the carburetor to warm up the engine. You will find your engine is slow to start and will not stay warm.
Bottom line: Leave your AC vents open!
If you want a healthy AC, a comfortable home and reasonable energy bills, you should always leave your AC vents open (even in unused rooms).
AC Vent Open or Closed: What Experts Recommend
Experts generally recommend keeping your air vents open to ensure optimal performance of your HVAC system. Here's why: Balanced Air Pressure: Keeping vents open maintains balanced air pressure in your ductwork, allowing your HVAC system to run more efficiently.
The cost to replace a purge valve varies based on the vehicle's make and model, the valve's location, the type of valve, and labor cost. On average, the cost ranges from $100 to $500 but can go higher for luxury vehicles.
The evap vent vale is a normally open valve. So applying voltage causes it to close. It allows fresh air to enter the canister. I'm all good with that.
We recommend keeping vents and interior doors open as much as possible for the best airflow.
Bleeding and venting valves remove or admit air or gases automatically from/to tanks, vessels or pipelines. They are float-controlled valves which close as the liquid level rises and open as the level falls.
Sometimes you may find that even with an air admittance valve, there are still clogs and a sewer odor. While this is rare, it is possible. Remember that these valves should last anywhere from 20 to 30 years, so if they are only lasting for a couple of years, there may be some problems that need addressing.
According to the “3% rule,” the pressure loss along the inlet piping should be kept below the 3% of the PRV set pressure (and at the rated flow capacity). Similarly, the “10% rule” was established for the maximum allowable backpressure.
A relief valve opens when static upstream pressure is higher than the opening pressure, and it opens in proportion to the pressure increase. This type of valve is more often used with incompressible fluids.
A pressure relief valve is a direct-acting device, which means pressure acts directly upon the internal components of the valve. Pressure relief valves are normally closed, with internal components held in a position that creates a seal to prevent flow.