I have been trying to come up with the best way to add adjustable pre-infusion and have come up with an idea and want to run it by the more electronically advanced members to see if it will work.

The system is centered around an On Delay Timer like this one: http://www.eagle-signal.com/content.aspx?id=79

What I envision is having the timer sense when I start the brew and then start counting down. The brew switch would be connected to the three way valve (to start line pressure water flow) and the countdown timer. The output of the timer would be connected to a SSR. The other side of the SSR would be connected to the pump.

This is what I think should happen: I turn on the brew switch, the water flows at line pressure. After a predetermined time, the timer turns the SSR on which engages the pump. Now the water flows at pump pressure until the brew switch is turned off.

Will this work?

Yup - exactly what I'm planning to do.

Alternatively you can wire it to a switch and have "manual" preinfusion for however long you want

My first thought was a separate switch but I like repeatability, so the timer would be better!

Some electronic timers have a remote adjustment capability. You could install the timer in an appropiate place and wire a pot to the front panel of your machine, giving you control over the time delay without going back inside the machine.
KDM

I'd probably go for something that did fractional seconds. 3 might be too little, 4 might be too much while 3.6 is just right.

It's very easy to build a settable timer for this from a very few parts : a 555 timer, a potentiometer and a capacitor.

Get an adjustable delay on make relay. Snip the hot going to your pump, put the relay inline with it and set your delay time. I had one on my old two group Faema. Worked like a charm and the timer had an internal relay rated for much more than my pump used so no extra SSR was needed. Put it all in a project case and tuck it under the machine. You obviously have to have a plumbed in machine for the mains pressure to do the preinfusion.

I'm hoping to get some feedback from the electrical type people.

Here is the timer's info sheet: http://www.eagle-signal.com/uploadedFil ... 6_spec.pdf

The salesman told me to connect constant voltage to pins 2&7, the input sense to pins 2&6, and the output to pins 1&3.

He said the timer could run the water pump but an SSR may be a better long term solution.

Any comments?

You will need a RESET on pin 5 to stop the pump. An SPDT switch with NC to 5, NO to 6 and C to pin 2 will do what you need.

The relay contact is 'probably' robust enough for the pump up to ~1/2HP.
OTOH, an SSR may not draw enough current to keep the relay contacts clean.

What is the current draw of the pump? A five amp rating without a specific motor h.p. rating is questionable. I would not use more then 50% (2.5amps) of the output spec for a motor unless horsepower rated. This is in line with standard ratings for switches and relays. Contacts used within their rating are kept clean by wiping action and will be happy with a low draw, within reason. For very low draw at low voltage special type (bifurcated and gold plated and/or gas filled enclosure) contacts are used.
KDM

I'm hoping to get some feedback from the electrical type people. . . . Any comments?

Yes.

Get an adjustable delay on make relay. Snip the hot going to your pump, put the relay inline with it and set your delay time.

This is what Dave Stephens did with his Faema and what Ken Fox did with his La Cimbali. Dave was working with a 240 VAC pump whereas Ken was working with 120 VAC. To properly "break" 240 VAC, you need to interrupt both "hots". That type of delay relay may be a tough find.

If it were me, I would insert a simple 240 VAC DPST switch to the external pump* and experiment to see whether this PI was worthwhile in your particular situation. BTW, KDM is a licensed master electrician (if I've read his previous posts correctly).

* by making up a cable/switch arrangement with quick disconnects similar to what the existing lines from the pump and/or machine have.