Ok, here it it. First off I'm self teaching myself how to program so bare with me. We have an existing Waste Neutralization system at our facility. We have 3 tanks. Pit A , Pit B, and Surge Tank. All of our waste throughout our facility dumps into Pit B, from there once the level in Pit B rises to a pre-determined level, it then transfers its level into the surge vessel which is basically a hold tank while Pit A is batched with Sulfuric Acid and Caustic to get the pH level in Pit A within the required range for us to pump it out.

Here is my question, I have been asked to add an addition valve (FCV_889) downstream from our existing dump valve (FCV_827) ,and add a additional second valve FCV_900 (Water Flush valve) that will be tee-ed into the tranfer line and flush the transfer line with potable water and clean and saturate our pH probe. So 2 new Valves will be installed. Once FCV_827 closes from either Pit A being empty or the pH range went "out of range" FCV_889 will remain open for 40 seconds, and Water Flush Valve FCV_900 will also open, but for 40 seconds. After 30 seconds FCV_889 closes, and after 40 seconds FCV_900 closes. ( the 10 second difference between the 2 valves FCV_889 & FCV_900 allows the transfer line to fill with clean water

I have uploaded the program files.

In the program file 5, "LAD 5 DIG-OUTPUT" on rung 7 you will see that when the B14:0 XIC bit is true Output O:10/7 is energized opening FCV_827.

I added rungs 8 - 13 for allow the valves (FCV_889, FCV_900) to Open / Close at the desired time 30 seconds and 40 seconds.

In rung 8, B14:0 XIC Latches FCV_889 open until it times out from T4:61 and unlatches in Rung 12.

Will rungs 8 - 13 do the job?

My fear is that once the XIO B14:0/6 becomes true, does what I want it to in the rungs following rung 9, it will be a "loop" until XIC B14:0/6 becomes true again.

Thanks for any help

John B.

I'm a little unclear about how this is suppose to cycle.

Both 889 and 900 open, then 30 seconds later 900 closes. At this point is there suppose to be a pause then open 889 and 900 again?

When Pit A pH is at its acceptable pH range. FCV_827 opens and FCV_889 opens. Both of these valves are in series with each other. FCV_827 is upstream from FCV_889.

FCV_900 however is tee-ed in between FCV_827 and FCV_889 it remains closed because its just a water source to flush (purge) the line after FCV_827 closes.

Once the level in Pit A is pumped below 500 gallons or a "out or range" pH reading. FCV_827 closes.

FCV_889 remains open for 30 seconds

At the same time FCV_900 (Water source) opens for 40 seconds

For 30 seconds both valves FCV_889 and FCV_900 are open flushing the line and flushing our pH probe.

After 30 seconds FCV_889 closes and FCV_900 remains open for another 10 seconds to fill the line to keep out pH probe wet.

Thanks.

I hope this explains it better

.

What you have should work. One thing I don't like in particular is the use of latch and unlatch instructions. For example 900 is on when T4:62 is incrementing. This is the Timer Timing (TT) bit

Thanks for the imput. maybe I'll rethink my use of the latches, but my real concern is that in rung 7 and 8

When B:14/6 XIC is true then FCV_827 opens, which is what it should do.

I have added B14:0/6 XIO to begin the process in rung 8. Is this the best way?

When B14:0/6 XIO in rung 8 becomes true it should do what rungs 8-13 need to do, but my real question is this.

Because the B14:0/6 XIO in rung 8 remains "true" after the process is complete , does rungs 8-13 just repeat themsleves on another CPU scan until the Pit A is full and ready to discharge and B14:0/6 XIC in rung 7 becomes true.

Maybe I'm reading to much into this.

Thanks for the help

John Bourg