Can too MUCH PSI be overkill

Discussion in 'Power Washing' started by chefwong, Mar 9, 2008.

  1. chefwong

    chefwong LawnSite Member
    from NYC
    Messages: 11

    I've been looking for a pressure washer for home use. Driveways, Siding, brickwork, car washing, etc. From my research, it looked like 3.K PSI was the ideal for concrete washing.

    Local Lowes has Simple Green PW solution. I gave them a call and was happy with the info they provided between their siding vs. concrete cleaner.

    For the machine, I've decided on the following + matching nozzle. Other than possibly a longer hose, is there anything out of the obvious I'm missing

    4GPM 3.5K PSI Belt Driven Washer

    Roto Nozzle
    Rotojet also seems to make 3-4 lines of turbojet nozzles not offered by Ptek.
    Any recommendations. General, Rotojet 3000 or 5000 Series, Rotomax, Suttner ??

    Should be useful to see how low I am attentunating the pressure ?
  2. Toy2

    Toy2 LawnSite Bronze Member
    Messages: 1,924

    I have a 2200psi from Sears, cleans brick homes, cars, trucks, mowers, decks, for me. Adjustable nozzle, will shred a towel in pinpoint mode.

    My buddy got a 3000+psi, his young son was running by him as he was washing his mowers, got hit in the face below his eye, cut it like a hot knife through much power for my needs...:nono:
  3. PLM-1

    PLM-1 LawnSite Bronze Member
    Messages: 1,640

    I have a 2500psi machine and to me, it's not nearly enough. My parents have a 3000psi and it would suit my needs better. The 2500 just doesn't have the power unless you are right on top of your target area. And if you are, the "cleaning area" is so small it takes forever.
  4. squirtgun

    squirtgun LawnSite Member
    Messages: 88

    PSI is relevant to the surface being cleaned.
  5. chefwong

    chefwong LawnSite Member
    from NYC
    Messages: 11

    The hardest surface I would be cleaning is

    - concrete driveway
    - stonework on the facade of the house
    - brick (which is not too hard)

    A better question, is I read a post where it suggested to keep the pressure washer at full PSI and just rate the nozzle/head accordingly.

    For example, on the rotary nozzles, if I have a PW rated at 3.5K PSI, and it's suggested that 3K + is ideal for concrete, do I buy a nozzle rated at 4K ?

    The same goes for the stonework . Without an extension wand, do I buy a nozzle rate at 2.5K ?
  6. squirtgun

    squirtgun LawnSite Member
    Messages: 88

    IMO, a turbo nozzle is not a wise investment.I don't own one and have been in buisness over 5 yrs,They have there uses,but I haven't found anything I can't clean using regular qc tips.
    If you plan on dealing with Bob he can tell you what over sized tips you will need to clean various surfaces.Since the gpm on my machine is larger than what you plan on buying the tips sizes are different.

    S DIAMOND LawnSite Member
    from South
    Messages: 108

    Should be useful to see how low I am attentunating the pressure ?[/QUOTE

    There are many paths that lead to the road known as pump failure. Here are just a few reasons why.

    1) Tampering with the unloader. (Trying to get more PSI)
    2) Adjusting engine speed (over-speeding attempting to get more GPM)
    3) Overheating water supply (by pass mode to long)
    4) Insufficient lubrication (pump maint.)
    5) Inadequate water supply (pump starvation aka cavitation etc.)

    PSI is the necessary "FORCE" required to break the bond between the surface and the soiled area being cleaned. Depending on that surface (Garage floor vs. Wooden deck) will determine the force you will need. If you have a "TRUE" 3000PSI rig, then obviously that is too much for a wooden deck, but great for maybe a sidewalk. Changing tips (not angle of degree) but orifice sizes is NOT the best way to alter your pressure output. Physical distance from the surface (reducing impact), or a dual lance wand with a flow control valve will lessen the force and possibly the damage. The advantage of the D.W. is that the GPM is still there, but the pressure drops. GPM is the flow that is required to move you quickly through the cleaning process. This is what the PROs are usually looking at. It seems the key, however, is properly treating the surface with the "right chemical" to help expedite the process. Unfortunately, I don't power wash for a living, and this is just M.H.O.:) However, I do repair pressure washers, so I do know this...
    Chefwong, if you are going to pressure test your pump, and you should, because its a good bench mark where your pump's health is, do the following:

    1). Use a "known tip" (that's a new one, or good one) with the CORRECT orifice size designed for THAT PUMPS RATING.
    2). Make sure the engines RPM's is CORRECT. Yes, you will need a good tach.
    3). Make sure you have a good glycerin filled gage with adequate pressure overhead. (a couple 1000PSI over pumps rating, at least).
    4).Make sure you have adequate water flow from the garden hose. If your unit is rated at 4GPMs a minute, than you should be able to fill 4 gallons in one minute into a container with your pressure washer completely hooked up. (with or without tip. less messy without) Yes, time it. Rule of thumb: you should have at least 5GPM at your garden hose spigot anyway.
    5). Now, don't be alarmed if your unit is a little off from the "Factory" rating. That is normal. However if you have done the proceeding, and its off several hundreds of PSI, you may have a problem. Remember this, your new pump will need a small time period for break in before you get the best reading, and more importantly, you loose about 200PSI across the unloader when reading the test gage.

    I know there are some people who don't care, so if you do adjust your unloader know this:

    1) Follow the previous set up above.
    2) With the engine running, water flowing, and correct tip in place, slowly turn in the unloader screw, and watch the pressure rise. Release the trigger and note the back pressure. The back pressure is the PSI increase when you release the trigger and the unloader bypasses. ( HERE IS THE KEY. THE BACK PRESSURE SPIKE SHOULD NOT BE MORE THAN 12% OF THE OVERALL PRESSURE). continue with the adjustment (adjust and release) As you keep turning, you will reach a point where the pressure will not increase, but the back pressure spike will. Continuing to adjust past this point will be dangerous!!! {If your pressure washer is rated at 3000PSI, and all you can get is 2600PSI with an acceptable back pressure rating. THEN STOP. THAT'S IT. I have seen units come in (damaged of course) rated at 3500PSI with a back-pressure rating of 4800PSI. I'm surprised the hose didn't't burst.:walking:
    I hope this helps some. :waving:

    FCPWLLC LawnSite Senior Member
    Messages: 352

    Good post.....

    I do however, believe that using larger oriffice tips is ideal for lowering pressure. Dual lance is great if cleaning flat surfaces needing the angle. We shoot high Vinyl with zero degree tips but use large (40) oriffice to reduce pressure and can draw chem from downstream injector.

    Great advice on leaving the unloader alone except to properly adjust for rated gpm/psi.

    S DIAMOND LawnSite Member
    from South
    Messages: 108

    Thanks FCPWLLC. I do try to help. I do agree that the tip (orifice) change is the fastest way to alter pressure vs. flow, and it reads as if you definitely understand those dynamics.:) However, most homeowners and some "pros" tend to pay less attention to those details, and mistakenly replace their existing (original) tips with either under or oversized ones, not realizing the overall effect, that is until something doesn't seem right.:laugh: That's when I get to see them.:help::eek:
  10. blake101

    blake101 LawnSite Senior Member
    Messages: 581

    From what I have read you are saying that putting the wrong tip on it can damage the pump. Can you please explain, not guessing your information, I just don't understand.

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