I do not want to get into a contest, but I think it is important to understand my point of view. I understand Thup wants the valves to be on for 2 seconds and off for 8 seconds, and he wants #1 valve to be on when power is applied, thats why of the power up reset circuitry.
It is my understanding and the formula works for me that the timing calculations for the 555 in the astable mode is: t in seconds =0.693(Ra+2Rb)C. Since the pot and the 560k are in series as Rb we calculate
T=0.693((470K+2(1.06M)).47uf or 0.843 seconds.
If the capacitor is changed to 1uF or two 0.47uF then the pot in Ron H circuit will work, as will my design, only in my design the pot may be near
minimum resistance.
The LED in my circuit is turned on every ten seconds. Since Thup has a stop watch to adjust the the timing to 10 seconds I created the design.
I agree that using a microprocessor is simpler, but not everybody wants to
go thru the learning curve of the micoprocessor and purchase the necessary hardware to program it.
I agree that the mosfets have a much lower saturation voltage than the darlington transistors. Yet most 12 volt relays and selenoid valves will fully energize on 75% of rated voltage and total power consumption will
be slightly less with the darlington drivers.

 

K7elp60, you are absolutely correct about my timing elements. I have corrected the values, and have added the power on reset and monitoring LED, both of which, as you pointed out, are important. I intentionally left them out on the previous schematic because I was working on it after hours at work and was in a hurry to get home (where I now am).
Thanks for keeping me honest.

BTW, I have no problem with your circuit. I was just trying to improve on my original and simplify yours at the same time. And, as I said before, I have no problem with driving the valves with Darlingtons.