1. #1
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    Default PTO-based HRT System Relief Valves

    A couple rather specific questions:

    For those of you using PTO-powered HRT systems (Saulsbury design, Amkus Ultimate, XRT, etc)...

    First, how many pressure relief valves (PRV's) are incorporated into the system that would prevent the 400ish horsies powering the pump from delivering an unsafe pressure to the tool you are holding?

    I'm curious because I have learned our system only contains 1 relief valve per discharge, and no relief valve in the tool, the lines, or anywhere else (Amkus).

    Second, aside from Hurst's Sentinel device that alerts you to a maxed-out pressure situation via an audible tone, is there any other manufacturer that offers devices alerting users to a maxed-out pressure situation, or that the relief valve is in operation? I ask because as a user, I would like to know when the pressure reaching the HRT becomes dangerous. Actually, it would probably be more useful to know if a backup PRV is in use, if some type of alert were available. It'd probably be unrealistic to expect someone to react to a high pressure prior to the development of a dangerous situation. Why would this be needed? It would indicate a failure of the primary PRV to regulate the tool's operating pressure, which can have bad consequences.

    Anyhow, if users of such systems realize they have only 1 PRV per HRT/HRT line (i.e. the one set at or slightly above the system operating pressure), I would suggest that they strongly consider the safety implications of such a design and strongly consider adding redundant PRV's just above the operating pressure of the tool, but within the manufacturers safety margins.

    Additionally, based on any replies we get here, look into adding alerting devices that will tell you when a PRV has been activated and other such options.
    Last edited by Resq14; 05-10-2003 at 11:05 AM.
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    14,by any chance are you alluding to the incinent at CCFAS?I know a little on the background but would you E-mail me the specifics when you know the exact reason that allowed one circuit to go high?Thanks T.C.

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    Exclamation Why I posted this

    I am posting this for the safety of others who might have similar systems. While I know some might try to use this to bad mouth the tool manufacturer, I am more concerned about the systems being produced or in existence that have the potential to have such a failure.

    This is a picture of a spreader that experienced a failure of its piston cylinder.

    The spreader was crimping a door to establish a purchase point. Just as the tool "bottomed out," there was a loud explosion and the tool and parts dropped to the ground. No one was seriously injured, despite the fact that a couple of big hunks of cast aluminum were sent flying. One landed on the other side of the car.

    Why did this happen? The relief/operating valve that determines what pressure the line is charged to did not operate as intended. There is only 1 such valve per line. Therefore it was possible for enough pressure to be sent to the tool to cause it to fail. Keep in mind there is a 3:1 safety ratio for this 10,500 spreader. I am still amazed that another component of the system didn't fail before the tool. We don't know how high the pressure actually got, or how high it is capable of getting. Post-failure, the pressure went to 12,000psi in less than a second.

    The tool failure was secondary to the valve failure. Please, please, please try to understand this. It wouldn't matter if it was a Holmatro, TNT, or any other tool. With the GPM's and PSI of the hydraulic fluid that PTO systems are capable of producing and generating, no tool can withstand such forces.

    I insisted on backup safety valves being installed on everyline to reduce the likelihood of this happening again. The manufacturer and their reps were great about this, and they were promptly installed. We're still a little gun shy (understandably), but with the modifications I now trust the system as I did before this happened.

    So, to re-iterate my point: if you own a PTO-based HRT system, get backup valves installed per line. Typical portable HRT pumps would stall before ever reaching such pressures. When you have 500 horsies doing the pumping though... something else will fail far before the engine stalls.

    Also, I will never EVER operate a tool without being in full PPE. Luckily no one was seriously injured.
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    Last edited by Resq14; 07-13-2003 at 01:40 AM.
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    It has been quite a while since our Amkus 32" spreader "failed", and we still have no cause as to why the pressure spiked.

    Just figured I'd bring it up again in case anyone cares. I have a great picture collection if anyone is interested.
    Last edited by Resq14; 11-14-2004 at 02:33 AM.
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    14,What's up with that.It was my understanding while talking to the factory reps at NEFC Springfield that you guys had identified the causal factors and that modifications were forthcoming to retrofit all of these units.Not happening? T.C.

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    Resq14, I have included that picture in some of my training in the past as an example of why to wear full PPE. I could not remember where I had gotten the picture from though, thank you for reminding me.
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    I question the 3:1 safety factor mentioned - my bet is that the safety factor is 2:1 at best.

    The use of third party pto systems is not a good thing, as proven here. This incident also shows the importance of having tools tested to the NFPA 1936 standard at the pressure they operate at. I am aware of some tool manufacturers that claim to be NFPA 1936 compliant yet they test at 10,000 psi and operate at 10,500.

    Keep in mind, most if not all "universal" pto systems are not tested to NFPA 1936. When you buy tools, you should buy them as a system, all testing to the standard.

    Finally, pressure relief devices in the tool is critical. My bet is that this tool did not have any and a castastrofic failure occurred.

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    The use of third party pto systems is not a good thing...
    the importance of having tools tested to the NFPA 1936
    rescuemaster do you work for one of those manufacturors?

    this was not a 3rd party PTO, this system was 100% Amkus Ultimate system, installed per Amkus specs at the factory, and serviced by Amkus. All the parts that failed were Amkus. As far as NFPA compliance it would not have helped here, the failure resulted in somewhere in excess of 20,000psi, perhaps as much as 30,000psi before the tool failed. No testing or certification would have caught this.

    What this is a good example of is that despite advances with automation that make the trucks easier to operate, we still good old fashion guages and a set of eyes to watch them. Even better would be a high pressure alarm that could be heard over the engine.

    14's point is that this could happen to any PTO based system. High horsepower, high volume pump, and a failure of the pressure regulator will result in enormous pressure spikes in the entire system.

    Imagine if your fire pump governor were cranked up to 400psi and you had the pressure relief valve set to 150psi. If the relief valve failed what would happen? If doesn't matter how many ISO NFPA and OSHA certifications the pump has its gonna give the guys on the nozzle a ride. At least in that example you have a gauge to watch, in our system we don't.
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    Fire304 - I apologize for not realizing you were using the "ULTIMATE" ( apparently not ) system.

    Your post began with ..."For those of you using PTO-powered HRT systems (Saulsbury design, Amkus Ultimate, XRT, etc)... "

    Perhaps manufacturers should design these things better. I would have thought that the pumps would have restrictions as to their maximum output pressure, like 10,500 psi. From my experience, if you increase the rpm ( you refer to horsepower ) on these or any hydraulic pump, the pumps normally cavitate and you end up with less flow and pressure.

    Since this was a Amkus design, I do question why they do not test their products to NFPA 1936. I bet you required the truck manufacturer to meet NFPA, and perhaps the gear you wear.

    And no I do not work for one of those manufacturers.

    Just a thought,

    Hopefully this will not happen again and thank goodness no one was hurt.

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    My apologies RM, your enthusiasm for the NFPA testing sounded like a sales pitch, and I was a bit off the day I last wrote on.

    For what its worth, when not exploding in your face (that was an attempt at humor) the Ultimate system is very impressive to work with, especially coming from using a 5hp Honda pump, the speed which the tools operate at (and my understanding is that the other PTO based systems are similar) is about 4.5 times faster than a stand-alone pump.

    The PTO pump actually is (as I understood it) a standard hydraulic pump, on our system the same pump also runs our Harrison generator. The failure in our system was of a portion of the system that multiplies the pressure from the pump (can't recall if it was called an amplifier or booster or something like that). Its a small block (machined in Germany as I recall) where volume goes in one end and pressure comes out the other. Again, I'm working from memory of over a year ago, but as I recall it was a multi-stage device so the hydraulics were boosted over a couple of steps. It was the final stage of this device that was replaced to repair our system (we have yet to hear back from the rep as to why or how it failed). Once the pressure leaves the booster it runs through a pressure relief valve and a solenoid before going out through the hose to the tool. One of our boosters "jammed" in the full boost mode, initially the pressure relief probably did its job, but eventually it also failed (as a direct result of the constant excessive pressure). When that happened the tool began receiving too much pressure.

    The failure occurred while the tool was being closed, the jaws had clamped down to about 1-2 inches from fully closed and stopped moving with the hand valve in the "close" position allowing full pressure to build in the piston. BANG. Had the tool not jammed on something solid we would never have known.

    Since the hydraulics are not something that gets tested annually you could have this problem too, we may have had it for months, even a year or more, the right conditions to blow the tool never occurred. NFPA testing requires that we test our LDH to 200psi, if we put 400PSI into the LDH the NFPA testing would not have helped one bit, I really don't see it helping here. What is needed is some sort of warning device, as the system is "blind" there is no way to monitor its status. To date, only Hurst has installed a warning device, perhaps because they've experienced similar problems?

    I'm goona start another post to talk about the NFPA approval thing...
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    304,Hurst,as I'm sure you are aware,is a low pressure tool as opposed to our high pressure versions.I don't care who's unit it is,if pressure regulation fails you have the probability of a serious failure as evidenced here.The only workable answer I can see would be a redundant pressure relief so that a single failure could not over pressurise the system.I've also found that less experienced tool operators have a tendency of not knowing when to "quit"or repurchase the tool.These actions have a tendency to overload tools and I'm sure were a factor in your failure.And if I had to bet,I'd bet you a steak dinner that at about the time you heard the sentinel screech(if you had one) your tool would have still separated.That is to say conditions staying equal,the failure would still have occured.The sentinal operates at "peak"or just under.In this case "peak"was well over design limits.So where do we go from here?An interesting quandry to say the least.I know where you're coming from on the Honda.We had a low bed where I used to work that I converted from the Honda pump in the Gooseneck to the truck run wet system.Needless to say,the Honda didn't get much use after that.T.C.

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    Red face Certifications

    Let me put my cynical hat on for a minute…

    Ever been ripped off by a mechanic? I bet you he was an ASE certified Master Mechanic. Or how about dealing with a Better Business Bureau member who screwed you? Ever get an electrical shock from a UL listed item? Does your town really deserve its ISO rating? I don’t give a lot of credence to most certification processes. Usually the whole process was written by and controlled by the people who will make a profit off the certification process. The ASE was started by a group of mechanics who wanted to make a “standard” which they could use as a selling point. To a certain extent NFPA standards fall under this category. The sprinkler standards were written with the help of sprinkler manufacturers. The newest manning standards were written with much participation of the IAFF. I’m sure some of the HRT manufacturers were involved in the NFPA standard for them, probably the very ones who now posses the certification.

    How about the RIT standard? Not much there, hu? Now remember I have my cynical hat on, but perhaps that’s because there’s no money to be made with RIT yet so its not gotten much attention. The NFPA is a private organization, it is not a government body, it must make money to survive, and the certification process is part of that revenue stream. Even the UL is there to save insurance companies money and they make money doing their testing.

    Government standards have different motivations, but they are sometimes bogged down by the committee mentality, and even they are not immune to outside influence. I own an inflatable lifejacket that was designed by fishermen for fishermen and without a doubt it is the most comfortable life jacket I’ve ever owned. It is not however a USCG approved PFD. The manufacture states in its literature that the cost of becoming USCG certified would nearly double the cost of the jacket and the required modifications would ruin one of the best features of the jacket.

    This jacket’s inflation “ripcord” is attached to a 4"x6" patch of material that is Velcro’d to the jacket. It looks like the left breast pocket. You grab any portion and pull about 6 inches to activate the CO2 inflator. Having it done this way means its easy to activate but also not likely to accidentally get snagged while working. The USCG required manual activation to be done by a bright yellow plastic "T" handle labeled with red lettering that says "PULL TO ACTIVATE", that it hang free, may not be concealed while being worn, and must activate with 2 inches of travel. The problem is that this handle gets caught on something and before you notice you’ve moved more the 2 inches and the damned thing inflates on you (I've actually seen this happen once on a sailboat, quite funny).

    If they got it approved they could sell a lot more, but then the price would have to go up to make back the cost of the approval process which means fishermen might be less likely to buy them and not help the performance of the jacket at all.

    All certification processes cost money and time. In order to receive such a certification a manufacturer usually has to get independent testing, product design review, product manufacturing review, monitoring, torture testing, destructive testing, a pile of documentation a mile high, and in the end you get a little sticker you put on the product which says "approved." Since there is no requirement for HRT's to be NFPA compliant (unlike our turnout gear which must be according to my state's laws) there is only a small advantage of a sales pitch item with no real benefit to the tools.

    There are exceptions, I think highly of UL ladder testing every time I scramble up one, and in the complete absence of certifications there would be chaos. Just remember there is money being made off of all certifications and that influences the whole process.

    Removing cynical hat now.

    101, the problem with a redundant system is that you can still have the same failure, you just have more time before the 2nd relief valve fails. With no warning device there is no protection from a cascading failure. A simple pressure activated switch hooked up to a light and buzzer on the pump operator panel (perhaps with a 2 second delay to ignore spikes) is the answer.
    Last edited by Fire304; 11-14-2004 at 03:14 PM.
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    Originally posted by Fire304
    The failure in our system was of a portion of the system that multiplies the pressure from the pump (can't recall if it was called an amplifier or booster or something like that). Its a small block (machined in Germany as I recall) where volume goes in one end and pressure comes out the other.
    Amkus calls them intensifiers.
    Originally posted by Fire304
    One of our boosters "jammed" in the full boost mode, initially the pressure relief probably did its job, but eventually it also failed (as a direct result of the constant excessive pressure). When that happened the tool began receiving too much pressure.
    The intensifier works with an integral relief valve... when you reach the set operating pressure, it dumps excess to the return side. This is how the maximum pressure is set, and how excessive pressures are prevented. Initially the technician was curious if anyone had been tampering with the pressure adjustment screw. Since it was under a piece of welded grating which conveniently prevented such access (and for repair work, was also nice and "convenient"), it was incredibly unlikely it had been tampered with. Speculation was that a foreign object or a piece of the system became trapped in the pressure regulating assembly... again, speculation.

    Flow (gpms of fluid, which translates into speed) can also be controlled in addition to the pressure.
    Originally posted by Fire304
    What is needed is some sort of warning device, as the system is "blind" there is no way to monitor its status. To date, only Hurst has installed a warning device, perhaps because they've experienced similar problems?
    I agree that it would be nice to know, however, it does you little good due to the speed at which the system can build pressure. With the horsies behind it, the system can build pressure way faster than you can safely react to an alarm, flashing light etc. I stood there that day and watched the pressure hit 12,000 PSI and skyrocket up... the reaction time of the technician was the only time wasted in shutting it off.

    The solution, imho, which we also implemented, involved separate relief valves per line. A good addition to this would be an alarm telling you when the backup relief valve kicks in. That way, you know that you are having a problem at the intensifier and need to get it checked.

    Service-wise, routine testing requires each circuit to be calibrated twice... the bakcup relief valves need to be set and checked at a slightly higher PSI than the intensifier... then, the intensifier per circuit must be calibrated and checked. Just adds some extra steps, but it is definetly necessary.

    I've had another theory on the failure but I'm still trying to confirm some things.
    Last edited by Resq14; 11-14-2004 at 02:27 AM.
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    Originally posted by Resq14
    the speed at which the system can build pressure. With the horsies behind it, the system can build pressure way faster than you can safely react to an alarm, flashing light etc.
    I would be willing to bet that in our case we'd been over pressure for some time, that an alarm would have kept pinging every time the tool came under a load. Remember it was a training session, the operator was not as experienced with the speed of these tools as we are. As Grandmaster 101 noted the tool failed because in this particular use it had hit something solid and a full head of steam hit the piston, the operator didn't know to stop cranking the tool. If failure occured between 20k and 30k an alarm sounding at 12k would have shown a problem. If we properly noted the alarm and checked a pressure gauge (both of which we don't have) we may have been able to catch all this long before the day of failure.

    I was also thinking like you (but did not express it) that the alarm should be between the two pressure relief devices. The problem of having no alarm now is that the intensifier may have failed again, as long as the 2nd releif valve works we'll never know, but eventually the relief will fail too and then we are back to tools blowing up.

    Just having a relief with no indication of failure is a stop gap measure. Under the same conditions eventually you will have a total system failure.
    Last edited by Fire304; 11-14-2004 at 03:14 PM.
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