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  1. #1
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    Default High vs Low pressure HURST

    What is the difference between a high or low pressure set of Hurst tools? or even just any set for that matter?
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    MembersZone Subscriber AC1503's Avatar
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    Hurst named equipment operates at 5,000 p.s.i.

    Hurst bought out Lucas. The renamed the Lucas line as Centaur. The Centaur equipment operates at 9,135 p.s.i.

    All other high pressure systems that I know about operate at 10,000 or 10,500 p.s.i.

    The low pressure and high pressure systems should produce the same force, given comparing apples to apples.

    The higher pressures allow for cylinders that have a smaller surface area. Thus being small in size, the tend to be lighter in weight.

  3. #3
    Forum Member Rescue101's Avatar
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    One difference not related to operational qualities is the Transformer spreader with the changable jaws.This allows up to a 40" spread and is NOT available in hi pressure.Also the controls are different in both sets.Construction and weight is also different?Confused yet?Try both sets. T.C.

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    AC1503 IS CORRECT. LOW PRESSURE OR 5000 PSI SYSTEMS HAVE TO HAVE MUCH LARGER PISTONS AND VALVING WHICH MEANS A LOT MORE WEIGHT. ANOTHER DRAW BACK TO LOW PRESSURE IS THEY CAN'T GET THE HIGHER CUTTING AND SPREADING FORCES THAT 10,000 PSI SYSTEMS GET. I THINKWE ALL KNOW THAT 5000 PSI FLUID IS NASTY AT BEST.

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    Low pressure systems are generally run on Phosphate ester fluid which has excellent flow characteristics at temps down to below zero.Most hi pressure systems use a mineral based fluid which has different operating charateristics.Mineral oil for generic purposes is "standard"hydraulic oil.Most hi pressure rescue tools use a "tricked"out version of standard hydraulic oil.Operationally you generally won't see a huge difference in either system. T.C.

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    A low pressure system has become available for a reasonable price from another dept in illinois that just got a new set from FEMA. In general some parts of the system are older but some are newer in the last 6 years the power supply was replaced with a 5hp (i believe it was 5) and within the last 3 years they have replaced like 300 feet of hose. They are including the cutters, spreaders, and a hydralic ram, all of which can be run at the same time from one unit.
    "Let's Roll." Todd Beamer 9/11 first soldier in the war on terror

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  7. #7
    dazed and confused Resq14's Avatar
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    Originally posted by AC1503
    The higher pressures allow for cylinders that have a smaller surface area. Thus being small in size, the tend to be lighter in weight.
    ...which is typically offset by the thicker cylinders and components needed to maintain strength tolerances with the higher pressure.

    Amkus 30CX 32" Spreaders (10k psi)
    Max Spread Force: 16,950 lbs
    Weight......47.5 lbs

    TNT Rescue S-100-32 32" Spreaders (10k psi)
    Max Spread Force: 27,684 lbs
    Weight......56.3 lbs

    Centaur S28 362C331 31.5" Spreaders (9k psi)
    Max Spread Force: 51,700 lbs
    Weight......55 lbs

    Hurst ML-32 32" Spreader (5k psi)
    Max Spread Force: 16,000 lbs
    Weight......52 lbs

    Holmatro 3242UL 32" Spreader (10k psi)
    Max Spread Force: 12,925 lbs
    Weight......42.5 lbs

    Genesis S60 XL 32" Spreader(10k psi)
    Max Spread Force 55,125 lbs
    Weight......54.9 lbs

    It's hard to say that operating pressure alone makes makes a tool heavy/light, based on the above.
    Last edited by Resq14; 01-03-2005 at 10:39 PM.
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  8. #8
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    resq14 you forgot a couple among others

    Genesis S40 XL 28" SPREADER(10,500 PSI)
    MAX SPREADING FORCE 29,000 LBS
    WEIGHT 43 LBS

    GENESIS S60 XL 32" SPREADER(10,500 PSI)
    MAX SPREADING FORCE 55,125 LBS
    WEIGHT 54.9 LBS

    GENESIS S35 24" SPREADER(10,500 PSI)
    MAX SPREADING FORCE 25,000 LBS
    WEIGHT 35 LBS

  9. #9
    dazed and confused Resq14's Avatar
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    Trying to compare apples to apples, with 32" spreaders...
    so this one would be comparable:

    GENESIS S60 XL 32" SPREADER(10,500 PSI)
    MAX SPREADING FORCE 55,125 LBS
    WEIGHT 54.9 LBS
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  10. #10
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    Check that Centaur S28 weight again... 43.2# according to the website and literature.

    What is "nasty" about Phosphate Ester? This should be good!

    Tell the truth, it helps out in the arguements.

  11. #11
    dazed and confused Resq14's Avatar
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    Notice there are 2 S28's... one is listed as 31.5" and the other 28"... I think it's a mistake with model number. That is why I added the extra manufacturer's number. The one you're referring to was 28.4".

    http://www.hurstjaws.com/products/centaur_spreaders.Asp

    Again, I was aiming for a comparison amongst 32" spreaders from these companies.
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  12. #12
    Forum Member MetalMedic's Avatar
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    I wish I had the time to find the two or three other times I have posted a response to this same question...

    Low pressure tools operate in the 5000 psi range while high pressure tools operate in the 10,000 psi range.

    Low pressure tools and high pressue tools can sort of be compared to a pump on a fire engine. A two stage pump has a volume and a pressure function. With that in mind, think of the two tool designs this way. The low pressure tool accomplishes work through the volume of fluid it delievers to the hydraulic cylinder. The high pressure tool accomplishes work through the pressure that the fluid is delivered at.

    We can argue for weeks on here about what tools are the best. So let me make VERY clear that ANY hydraulic rescue tool, in the hands of a competent operator, will accomplish the task it was designed to do. All tools have advantages and limitations. You just need to work with your own tools in order to become proficient with them.

    What you need to understand when you are looking at buying hydraulic tools is that some tools will behave differently when they are actually working than they do when they are being demonstrated. You will hear a lot of hype about how some tools will open and close much faster than others. However, when you take the same tools and try to open and close them using the same loads, you may find that the "fast" tool takes longer to actually perform a task, while the "slow" tool will perform the task at the same speed as it did when it was not opening and closing under a load. I have seen this happen a few times, so be careful and pay attention to what you are seeing.

    I could get into some of the physics as to why this happens. But that won't accomplish much here. If you want my personal opinion on what kind of tools I prefer, send me an e-mail and I'll give you my opinions. Same goes for fluid types... everyone seems to have their own ideas on what makes a good hydraulic fluid.

    Bottom line is that you need to find a tool that serves your needs. You also want to be sure that you buy a tool from a sales rep that will give you good service in case it needs repaired, preferably someone who has spare equipment to loan your department if you need to send the tool in for repairs.
    Richard Nester
    Orrville (OH) Fire Dept.

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  13. #13
    dazed and confused Resq14's Avatar
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    The physics behind it are very simple:

    A larger piston requires less pressure to produce x-amount of force,

    while

    a smaller piston requires a larger amount of pressure to produce the same x-amount of force.

    Pressure is exerted over the surface area of the piston. The more surface area there is, the less pressure that is needed.

    While you might think a higher pressure tool will always be lighter because it uses a smaller piston, just remember that the thickness of the metal must also be greater because of the higher pressure. Thus, weight is more of a proprietary issue: the numbers speak for themselves.

    It's not really a pressure/volume issue. Increase volume in terms of flow per minute increases the speed of any tool. This is traced back to the HRT pump.

    A simple search of this category for "pressure" will show allllll the times we've discussed this in the past.
    Last edited by Resq14; 01-06-2005 at 04:32 PM.
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  14. #14
    Forum Member MetalMedic's Avatar
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    Originally posted by Resq14
    The physics behind it are very simple:

    A larger piston requires less pressure to produce x-amount of force,

    while

    a smaller piston requires a larger amount of pressure to produce the same x-amount of force.

    Pressure is exerted over the surface area of the piston. The more surface area there is, the less pressure that is needed.

    Yep.. that is the simple explaination... although you still need greater volume to fill the larger piston cylinder. You can also add to that the behavior of high pressure hydraulic pumps and low pressure pumps and how they cycle in order to obtain working volumes and pressures when a demand is placed on them. You can also talk about fluid reservoirs and heat disapation comparissons between high and low pressure. You might also want to talk about fluid characteristics and friction loss. Those are some of the the not so simple physics I don't feel like trying to explain in a discussion forum.

    While comparing high pressure and low pressure to a two-stage fire pump is not totally accurate. It is close enough to help someone understand the difference without going into great detail.
    Richard Nester
    Orrville (OH) Fire Dept.

    "People don't care what you know... until they know that you care." - Scott Bolleter

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