PDQ Laser 4000 u/c issue

[washnvac]

Got a unit where all the products from the solution pump and sf pump are running back through the under carraige. Since there are no check valves on either the hp or u/c line out, I assume it is one or both of the lexair valves allowing the product to scoot around those valves. I guess there is no check valves because I could not locate an hp check at 1 inch with hp capabilities. But that would keep the back pressure off the lexair valve. I guess I could reduce to a 3/4 inch check.

Still on a learning curve with this place I bought at Sheriff's sale.

Thanks in advance for any help.

 

[madscientist]

Well, there is a 3/4 inch check valve up above that the lp products go through on their way out to the bay, but that won't be the problem here. I would check the weep line check valves. There should be two of them, one above each Lexair valve.

 

[washnvac]

Already checked and replaced those. There is zero product coming back through those; so they are holding. I will probably just experiment with taking one of the lexair valves apart to see what's happening inside. Hopefully something simple will jump out like an o-ring or spring. Then hopefully, it goes back together. I have to have bleed through on both of them though, for product to come out the under carraige.

 

[madscientist]

Is it bleeding through to the u/c while those products are being applied on a car? At any given time, one of those Lexairs is always open. During a wash, the overhead Lexair will be open, and the u/c Lexair should be sealed closed. If it's not sealed properly, you would also have water coming out the u/c during the hp rinse cycles.

When you unscrew the front part of that Lexair valve, there is a spring in there which you should try not to lose when the 15 gallon wave of water sprays all over your chest. It's been my experience, when the spring is broken, that the Lexair won't work (open) at all. When that happens it causes the motor running the hp pump to trip it's breaker.

If the u/c Lexair valve is just not sealing you would certainly have hp rinse coming out of your u/c as well, during the wash cycle.

 

[whitescout]

Is the chemical coming back through the undercarriage during low pressure only? If so,

I would check the mac valve, to make sure that it id functioning properly. If it is not, there is no way the lexair valves can work properly. Turn on and off, output number 20 to check this, or you can manually work the mac valve by pushing the small white "button" on the side. Make sure your air pressure to the mac valve and ultimately the lexair valves are at 10% of the pump pressure.

If some chemical is geting by during HP also, I would check the dan foss valve for HP sealant, and HP drying agent. One of those is stuck open and feeding back to the inlet side of the HP pump.

 

[washnvac]

Yes, to clarify--I am getting all cycles back throught the u/c. It is not enough for the solutiuon pump or the hp pump to have any pressure loss. It is just streaming out of all the u/c and side blaster nozzles.

But for it to do this, it has to be leaking through on both lexair valves. First the hp, then over to the u/c. Also, the u/c has a small delay in it now, because all the water is bleeding down after a wash. So I am thinking I will start with the u/c lexair and see what I have. I assume there is a rebuild kit availbale for these somewhere? If so, where do you guys get them? Do not see it in kr book.

Thanks for the responses.

 

[dreese]

I would first shut off water feed to your weep to be sure it's not coming from there. The Lexair valves are normally open, air operated valves. Getting bleed thru at the undercarriage typically means the u/c valve is not closing fully. Make sure you have around 100 psi of air going to the Mac (changeover) valve. Clean the brass exhaust diffuser (cone on bottom of valve) with compressed air to be sure of a good changeover. Then, disassemble the u/c Lexair - inspect the seat in the body of the valve for wear, replace valve body if nicked. Clean / lube / reassemble the valve and test. If needed, rebuild kits are available thru your PDQ distributor.

 

[MEP001]

So I am thinking I will start with the u/c lexair and see what I have. Hopefully something simple will jump out like an o-ring or spring.

As a rule, nothing will be really obvious, but while you have it apart make sure the inside is clean of any scale, the seats aren't eroded, and lubricate it well when you reassemble it.

 

[ken-pro]

Inspect the 1" check valve inline with the undercarriage spray bar. Its only purpose is to add enough restriction in the U/C line to prevent siphoning / line emptying. This is a special check valve with high cracking pressure (Strong spring)

 

[washnvac]

Why can't a 1 inch dema high pressure electric solenoid be used in place of the lexair valve(s)?

 

[ken-pro]

PDQ and Washworld both use 1" danfoss dual port Solenoid blocks for the UC/arch changeover valve now.