before this, i thought that the delta pressure of a pressure switch was set at 10 psi and cannot be adjusted. what can only be adjusted was the low psi setting. my understanding was wrong. you can adjust the delta pressure by independently setting the low and high psi setting of the pressure switch. below is my notes on how to do the adjustment ...

A. why the need to adjust the setting:
my daughter complained that the motor of the water pump does not always start to run when the water in the pressure tank was already at a low level.
after checking the pressure switch, i notice that the small spring that controls the delta pressure (pressure difference between high and low psi) has lost it's tension and needs to be replace. problem is i cannot find a replacement spring here in marbel.

temporary solution while looking for a new spring, is to increase the delta pressure so that the small spring gets compress more for it to work properly.

B. take note of current setting:
before doing any adjustment. write down the current setting of the pressure switch. you will need this info in your adjustment task.
- low psi setting for the motor to run ... e.g. 20 psi
- high psi setting for the motor to stop ... e.g. 30 psi
- diff between high and low is the amount of psi at which the motor pump will run.

C. pressure switch parts:
a pressure switch basically has 2 parts:
- the relay to switch on the power to the motor pump ... e.g. SPDT relay for a 2-wire motor pump
- the pressure switch, the big part of unit ... it has 2 springs
the big spring for the low PSI.
the small spring for the high PSI.
there are markings on the plate to denote how to turn the nut screw that holds the spring to adjust it (+) upward or downward (-).

D. how to change the low and high psi settings:

[1] if you need to adjust both the low and high psi setting, then start first with the low psi setting. for my case, the current low psi setting is 20 psi and i want to lower it to 10 psi.

[2] before turning the nut, mark (use a permanent marker pen) one side of the nut with a permanent market. this way, you'll know when you made a full turn of the nut. for starters, lets just assume 1 full turn of the nut = 1 psi change (up or down).

[3] take note of the direction of the turn to reduce the psi based on the + and - mark. i initially turn the nut 5 times (to lower psi low setting by 5) in the direction of the (-) sign to determine the new low psi setting for the motor to start.

[4] after making the change, next thing to do is to to wait at which low psi reading will the motor pump start to run.
- you can either wait for the water in the tank to be use or you can simply remove (e.g. open a faucet) the water from the tank until the motor pump starts to run.
- once the motor starts, take note of the low psi reading. with 5 turns of the nut, the psi will be somewhere between 20 and 10 psi. with the info, you will be able to approximate how much psi was reduce with 1 turn of the nut.
- again adjust and turn the nut X number of turns until you reach your target low psi setting. once you made new the changes, wait again for the motor pump to start and note the psi low setting.
- do this step until you get your desired low psi setting.

[5] once you have set the low psi, it's time to adjust (if needed) the high psi setting at which the motor will stop running. initially, this is already set by the difference between high and the new low psi setting. so you already know at which psi the motor stops running.

[6] for my case, the difference was 10 psi before, so with a new low setting of 10 psi, the motor will stop at 20 psi. so if i want the motor to stop at 35 psi, i need to increase the high setting of the small spring by 15 psi.
Note: most local pressure tank has a max rating of 45 psi. so do not set the high psi setting too close to this max value.

[7] before adjusting the high psi setting, its better to completely drain the tank of water to remove all the pressure so that you can accurately set the high psi setting. unplug the motor pump from the AC outlet when doing this so that the motor will not start.
- once the tank is fully drain, adjust the nut (also mark one side of the nut to know 1 full turn) of the small spring. for starters, lets just assume 1/2 turn of the nut = 1 psi change (up or down).
- for my case, i initially turned the nut 4 full turns in the direction of the + mark which should be more or less = to a +8 psi change in the high setting.

[8] plug the motor pump and determine at which psi it will stop. turn to adjust the nut of the small spring based on the + or - marking to adjust the high psi setting. for my case, the target is 35 psi.
- in case the motor stops at a psi lower than the target psi, adjust the nut accordingly.
- in case the motor is still running after it has reach your high psi setting, simply turn the nut of the small spring to the - direction until the motor stops.

[9] after making the changes to the high psi setting, next thing to do is to wait for the motor pump to start and then stop at the new high psi setting.
- you can either wait for the water in the tank to be use or you can simply remove (e.g. open a faucet) the water from the tank until the motor pump starts to run.
- once the motor start and then stop, take note of the high psi reading. with 4 turns of the nut, the psi will be somewhere between 20 and 35 psi. with the info, you will be able to approximate how much psi increase with 1 full turn of the nut.
- again adjust and turn the nut X number of turns until you reach your target high psi setting. once you made new the changes, wait again for the motor pump to start/stop and take note the high psi setting.
- do this step until you get your desired high psi setting.

from the above, a new low and high psi setting for the water tank pressure switch has been set. i would also recommend that at least once a month you completely drain the tank of water/pressure so that you maximize the water capacity of the tank per psi. the reason why you need to do this, especially if your water source is a deep well, is because, sometimes the water in your deep well is not that good and on this scenario, the motor pump is putting both air and water into the tank. so if this scenario happens a lot, then the tank will have more air than water at any given psi. so it's really better to completely drain the water tank of its pressure and water once a month.

hope this info helps other members who are also using a motor pump and pressure tank for their household water supply ... cheers

Boo!