Oil Filters

Discussion in 'Mechanic and Repair' started by givey51, Apr 24, 2004.

  1. givey51

    givey51 LawnSite Member
    Posts: 2

    I have just found 6 fram ph8170 oil filters in my storage bin. Can anyone tell me if they go to the hydro unit on an exmark turf tracer HP? I know the exmark part number is 513211 but is the fram perhaps an alternative?
     
  2. fixer67

    fixer67 LawnSite Silver Member
    Posts: 2,100

    From what I can get Fram does not make hydro filters. Oil filters but not hydro filters. Check all the cars and trucks you own or have owned it may be an oil filter for one of them. I know a man who got a bath in hydro fuild when an oil filter he used in place of a hyrdo filter split. "There she blow!" Hydro filter casings are a lot thicker than oil filter casings. Now here is a question of my own on hydro filters. Why are the hyrdo filters on the return side of the system on almost all systems? Trash has to go though the pump,valve, and what ever to get to the filter it get trapped? Now why is it not before(intake side) of the pump. Now in books it is shown on intake but on the macnines it is almost always on the return?
     
  3. xcopterdoc

    xcopterdoc LawnSite Senior Member
    Posts: 752

    The theory being that if clean oil is in the tank, then clean oil is picked up and delivered to the pump. That being said, the filter is on the return side due mostly to pressure. The hyd pressure on the return side is usually 1/2 to 1/3 of system pressure. A normal spin on hyd filter will blow if used on the pressure side. On more complex systems, the do have pressure filters and filters in the tanks.
     
  4. fixer67

    fixer67 LawnSite Silver Member
    Posts: 2,100

    xcopterdoc> It is just my way of thanking that the filter should be between the tank and pump on the intake side. There is no pressure there just vacuum. I guess the vacuum is just not high enough to pull the fuild though all the time( cold weather) and a pump running dry is bad news. But if you look at books and manuals on hydro systems it almost always shows it where I thank it should be. I guess that goes to show what looks good on paper does not mean it will work in the real world
     
  5. Tech Guy

    Tech Guy LawnSite Member
    Posts: 5

    Most of the units I deal with-newer hydro ZTR's, walk behinds and stand-on units- have the hydro filter between the reservoir and the charge pump on the Hydro pump. This filters all fluid being returned to the system by the charge pump and allows the reservoir to separate out particulates and air.

    There are two major differences in suction side Hydro filters and standard oil filters:

    1. Hydro filters DO NOT have a bypass- if they did and were clogged the bypass would open and flow contaminated fluid through the system and take the whole system out very quickly.

    2. The micron rating/ Beta Ratio of the filter- This is more exact than a standard micron rating- filters are not Absolute- some particles at that rating get by. This not a very easily findable spec for most filters.

    On the suction side the pressure (resistance to flow) /vacuum seen by the filter is limited. The charge pump pressure is in the same range as the oil pressure in most cars as well as full pressure lubricated small engines.
     
  6. xcopterdoc

    xcopterdoc LawnSite Senior Member
    Posts: 752

    On the contrary.. alot of hyd filters are attached to filter heads that do in fact have by pass valves. If the filter becomes clogged on the return side, pressure will quickly build and start breaking things. Most are equiped with a light that tells you when a hyd problem exsists. On small equipment like mowers and such, the filter is simply screwed onto a head. If the filter becomes clogged, the fluid, like electricity, will find the path of least resistance and continue to flow across the top of the head, never even bothering to flow thru the clogged filter.
     
  7. xcopterdoc

    xcopterdoc LawnSite Senior Member
    Posts: 752

    on all hyd systems with a filter on the return side, there must be a way for it to bypass. other wise the pressure will build on the pump side. What is taken from the tank must be returned somehow to the tank or something will give and be retuned elsewhere, like all over everywhere!
     
  8. givey51

    givey51 LawnSite Member
    Posts: 2

    Well guys thanks for the info. According to landscapers supply which is where I bought the filters, this is the filter they supply as a replacement for exmark part # 513211 hydraulic oil filter. It is now on the mower and if it blows my hydro unit I guess I will have to sue them..
     
  9. Tech Guy

    Tech Guy LawnSite Member
    Posts: 5

    I think there’s some slight confusion in terminology here. The filters are generally between the reservoir and the charge pump- not the case drain side- thereby not being a pressurized filter.

    The use of the term "Return" seems to be causing the confusion.

    The fluid exits the case of the pumps through a case drain. The pressure from the case moves the fluid to the reservoir, which settles out entrained particulates, air and also dissipates heat.

    After the fluid is in the tank for it's specified duration (dwell time), it is then drawn through a suction side, non-bypass type, filter by the charge pump.

    The theory in putting the filter after the reservoir but before the pump and without a bypass would be to have the operator experience performance degradation without dumping contaminated fluid through the system which would destroy the pump and motor in very short order.

    I double checked the hydro schematics for Exmark and Great Dane and they show the configuration that I just described.

    I agree with xcopterdoc that if the filter were on the case drain line it would require a bypass, but I have not seen this used in practice. He is also correct in his statement regarding bypasses in the filter heads. But these are not in-filter bypasses- those would destroy the system.

    Generally there are 3 potential placements of filters in commercial cutting applications:

    1. Suction filters- most common- filter between reservoir and charge pump-no bypass at filter. Not under pressure- only suction. Commonly used with pumps which have integral charge pumps. Stops fluid flow when clogged

    2. Partial flow filters- Filter is located after charge pump and after charge pump relief valve- uses the charge pump relief as pressure relief if clogged. This is less common- it costs more and takes up more space. Dumps fluid flow into case as relief valve opens.

    3. Full flow filters- Located after the charge pump but before the charge pump relief valve- it has its own bypass which directs the fluid to the case drain line and back to the tank. This is also not very common and requires more space and cost than the suction filter design.

    All of the above filtering methods are effective. It is important to know which one you need

    I'm glad you found out which unit your flter goes on.
     

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