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Iwata Hi-Line BH sluggish trigger

Discussion in 'Troubleshooting!' started by Sali, May 28, 2019.


  1. Sali

    Sali Double Actioner

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    Not sure if sluggish is the right term. Well, this is about my almost brand new HP-BH. The trigger was pretty stiff so I switched to soft spring. With soft spring the trigger does not come back or if does, it comes back in slow motion. I applied tiny bit of lube but did not improve significantly; I took out the piston O ring, cleaned it nicely (no strong solvents, never put any before too) but to no avail. It kind of works if I keep the PSI to say 20 or above and control the air velocity using airbrush MAC valve. Bottom line is, it is working but not as a $200 airbrush should work. The airbrush code says it was manufactured in October 2018 so it is not like it was sitting in storage for years.

    Should I order a new piston O ring? I guess #94I1451 is the correct part number. If I must, from where should I order it? Coast airbrush? The problem is, the part costs just $4.5 but shipping is $10.00. I was wondering if I also order the valve piston? Maybe the valve piston is bit rough hence more friction?
    Last edited: May 28, 2019
  2. DaveG

    DaveG Detail Decepticon! Very Likeable!

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    pm me your address again, and I will send you an o-ring
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  3. Sali

    Sali Double Actioner

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    Thanks so much Dave. I have put back the original spring in the air valve assembly. I noticed that sometimes the trigger remained depressed and it would eventually ruin that wonderful soft spring. I will try to wear out the O ring a little using the stiffer spring and see if it helps. Obviously the airbrush is not seeing as much use and maybe that’s part of the problem. Let’s see.
  4. DaveG

    DaveG Detail Decepticon! Very Likeable!

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    I buy the o-rings in bags of 100, i have more than a few ;) I have maybe 25 of the HP series brushes here, and I can assure you the trigger should not be sluggish no matter the spring you use (within reason). Lets replace the o-ring as see where we get. I can look up one of the older messages for your addy...
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  5. musicmacd

    musicmacd The Createx Bandit Very Likeable!

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    Never put lube on the plunger! Is gunks up and makes it the trigger sticky, use alcohol to clean off the lube and wait for Daves O ring!
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  6. JackEb

    JackEb The Dragon Hunter Staff Member Admin

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    I agree with MusicMacD, if the lube you have is the blue Iwata lube then throw it in your toolbox. For me it caused more issues than it solved.

    It’s possible the previous owner used something they shouldn’t have on the o-ring.

    Wait for Dave’s mail, you won’t regret it

    And never use anything on the o-ring , you shouldn’t need to
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  7. AndreZA

    AndreZA Elite Member! Elite Member! Very Likeable!

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    My HP-B, which I bought second hand, also had a very stiff trigger down. So changing to a soft spring also did not help. Even replacing the o-ring did not help. I then used the push pin, or whatever it is called that sits in the body between the trigger and air valve, from my Olympos HP-100 and it now works perfect, even with a soft spring. The Iwata pin in the Olympos also works perfect with a soft spring.
  8. Sali

    Sali Double Actioner

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    Thank you Dave. Like I mentioned, I am not 100% sure that it is the O ring alone. May be the piston valve is rough, who knows. If you have one in spare, can you throw in too? I will mail you back in case O ring alone solved the problem. Should I try to polish the piston valve to see if it works? Thanks again.
  9. Sali

    Sali Double Actioner

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    No, I have never used blue Iwata lube. And it is a brand new airbrush, and when I completely disassembled and cleaned it, no signs of any paint inside the body, only grease on the threads.
  10. Sali

    Sali Double Actioner

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    Yes, so I have requested Dave to throw in the piston valve too if he has one in spare. I may try to polish the piston valve to see if that helps. Thanks.
  11. DaveG

    DaveG Detail Decepticon! Very Likeable!

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    the tolerances on the valve pin are not so tight as surface finish should effect anything. Besides, brass on chrome is a good bearing surface... it has to be the o-ring against the push pin... Without use o-rings can dry out, and get pretty firm. Not a big deal at all...
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  12. Sali

    Sali Double Actioner

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    Hummm, you know, in the lab we tend to soak the neoprene O rings in methyl salicylate to soften them. I believe these O rings are also made of neoprene. Should I soak the O ring in the methyl salicylate to see if it comes back? Just a wild thought.
  13. DaveG

    DaveG Detail Decepticon! Very Likeable!

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    yeah, buna-n o-ring (nitril) as long as you don't pick up too much swell on it, it isn't gonna hurt anything, at this point. I already have a new one in an envelope...


    here's a thought - remove the o-ring and see what the trigger does. If you use air, you will feel some of it come up through the trigger slot, but don't worry about it. You are just looking for the "feel"
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  14. JackEb

    JackEb The Dragon Hunter Staff Member Admin

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    oh okay, in your first post you mentioned your "almost brand new HP-BH" which led me to believe it was a 2nd hand brush :)
    it will be interesting to see what difference Dave's o-ring installed
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  15. Justin Sane

    Justin Sane Double Actioner

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    Good to know! I would never have thought...so many recommend lubing the valve, it never really occurred to me that it may cause issues down the road.
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  16. JackEb

    JackEb The Dragon Hunter Staff Member Admin

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    I never lube anything moving, I just try and keep it super clean, I do however use k33 lube as a thread seal at the business end (chapstick also works)
  17. Sali

    Sali Double Actioner

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    There is a tool called a pipette; we use them a lot in labs. They have a metal (stainless steel) piston that runs through one or multiple neoprene O rings. The pipettes come with special white color lube and are highly recommended to use that lube to keep them functioning well. You see sensitivity and accuracy are at stake, for we use these tools to measure volumes as little as 0.1 micro liter. So what I am trying to say is, lubricating stainless steel pistons to move with least friction through rubber O ring is scientifically advised. In fact I wish to pass on some of this lube to Dave for him to evaluate and compare with other lubes.
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  18. JackEb

    JackEb The Dragon Hunter Staff Member Admin

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    If you want something tested then getting it to @DaveG's lab is a great start
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  19. DaveG

    DaveG Detail Decepticon! Very Likeable!

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    Trust me, I probably have the o-ring lube. I used to build high pressure containment vessels and pressure regulators that work in the range of 3000-45ooPSI. O-ring longevity, lubricity, and integrity were fairly important ;). The Clear Urea based lube I provide is absolutely the only lubrication any part of an airbrush will ever need. (Not a lube I used in my previous work). It is also completely unnecessary for a brush to work properly, and last a good long time - just helps.
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  20. Sali

    Sali Double Actioner

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    A big thanks to Mr Dave for sending me various parts to sort out the problem. It appears that the pin was faulty, very rough compared to one Dave sent me. It is obvious that the pin was grinding against the rubber and that’s what was rendering trigger action slow. Once replaced with Dave’s one, the trigger is smooth and feels great.

    You can see in the attached image that Dave’s pin (top) is shinier compared to the one came preinstalled in the AB (below).

    Again, thank you Dave.

    712ACF29-8BED-4736-8508-81B1020E255C.jpeg
    Last edited by a moderator: Jun 4, 2019
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