After the pump is shut off, open a faucet in the house and then begin pressurizing the tank. There is a schrader valve on the tank to insert air in. Add air until there is no more water in the tank and then bleed the air back off. The air pressure in the tank (EMPTY) should equal the pressure switch shut off point.
If it's a well water pressure tank, then just switch pump OFF and drain it through nearest faucet or the drain valve that SHOULD be fitted at base of the tank. Sometimes you may need to fit an air hose to the top 'sniffer' valve and pump a bit of air in with a small compressor to expel all water.
Release the pressure (safety) valve then open the drain cock. Close the valve and re-pressurize. Make sure you wear safety goggles.
Open the drain plug at base or the nearest faucet and connect a small compressor to the air nipple on top.
VERY Carefully not to cause an implosion
Unless the heater is relatively new, the drain is going to be slow and in some cases not work at all. Rust and sediment collect in the tank and plug the drain.
If water doesn't go into the pressure tank you will not have water pressure.
You switch off the pump, drain the pressure tank, then remove old gauge and fit new one.
If the tank, shut the water off and drain with a hose on the drain faucet on the bottom of the tank. The pressure relief valve can be replaced (however a PRV is meant to drip, it has to expand.), so can vacuum breakers and the TP valve.
remove the fuel tank and drain the water
Depends on your code. If you have a PRV or, as you would say, pressure reducing valve on your water supply to your house, you need an expansion tank. If your pressure is above 80 psi, you need a PRV AND an expansion tank.
Sound like maybe the bladder has burst in the tank and is covering the drain.
it should not be a water in oil tank it is mean engine cracked
depending on many different situations, your bladder in your pressure tank can be broke and it can still work if your pressure tank is vertical with inlet down and your bladder just has a hole or crack in it. Most of the times however with a damaged bladder the pre pressurized air inside the tank will over time leak into the water system and then your pressure tank will not work properly. Sometimes on pressure tanks that sit vertical and have a ruptured bladder the pieces of the bladder clog the inlet/outlet thus making the pressure tank fail and it can be a pain if its a bigger pressure tank to remove because it will not drain out the water. Most pressure tanks have a air inlet on top or opposite side of the water inlet/outlet and should always be precharged of air pressure psi depending on the amount of water pressure like example 15-18 air psi if water system is running at 55-60 psi. One way to find out if your bladder is broke or precharged in your pressure tank is to drain the water pressure out then put a air gauge on the air fitting of the tank and see if it has pressure.
Shut the water supply to it and drain it.
The pressure only depends on the height of water above the outlet. The width or height of the tank make no difference. (The tank may very well be 16-ft tall, but if the tank is empty, then the pressure at the drain is zero.) If the water is 16-ft high above the outlet, then the pressure is "16-ft of water". That pressure is also equivalent to: -- 998.82 pounds per square foot -- 0.499 ton per square foot -- 6.94 pounds per square inch -- 0.472 atmosphere -- 14.12 inches of mercury -- 35.87 centimeters of mercury -- 47.82 kilo-Pascals
Bottom of the air tank. Used to drain the water in the bottom off the tank