hydraulic power question and filter # help

jimandsuzy · December 29, 2008, 08:09:20 AM

I just replaced my rusted iron pipe power steering lines with flex hose. My old system had 1/2" ID lines and hoses except for the last 5' of hose which was 5/8" ID hose to the filter. The guy at the truck parts place said it was OK to just run all 1/2" ID. Now over the weekend I'm thinking why would someone have put the larger hose next to the filter. I remember from high school that going to a larger ID will reduce the pressure of a fluid. I also looked at some filter specs and they say about 700 PSI so I suppose that is why the larger ID hose is used. So I'm getting ready to go to the parts house to get 5' of 5/8" ID hose when I look at the connector going into the filter and it's ID is 1/2". So my question is does it do any good to have 5" of larger hose to reduce the pressure only to have it neck down to 1/2" at the inlet to the filter? Any fluid engineers out there? Also my filter doesn't have a # on it so I called Fleetguard cust. serv. and they say they can't give me a # from the dimensions which are 1 1/16" ID both ends, 5" tall, and 4" OD. Any idea how to find a part #? Sheppard (sp?) is the power steering unit. Thanks to all, Jim

OneLapper · December 29, 2008, 09:29:01 AM

Are you planning on running 1/2 2 wire hydraulic hose for the entire length of the coach? I just installed a oem power steering system on my 4106 and I used 3/4 hose and pipe throughout. The smaller hose will create higher operating pressures which increases temperature and airation of the fluid. I spent the extra money and when with the larger hose and pipes for the sake of longevity of the system.

Hope this helps,

Mark

Tom Y · December 29, 2008, 09:29:14 AM

Jim, I would think the filter is on the return at the tank? So there should be minimal pressure. Not sure I would bother going to 5/8 line if the rest is 1/2. If you had 3/4 fittings on the filter maybe it wold slow the flow thru it. Is it the return? Are you sure? And I have NO degree in this field, but have had some schooling 25 years ago. Pumps make flow, resistance makes pressure. Good Luck Tom Y

jimandsuzy · December 29, 2008, 01:06:50 PM

Mark, I bought 1/2" ID hose both ways because that was original equip. except for the last 5' which was 5/8" ID.

Tom Y, the filter is on the return side inside of the fluid reservoir and is the return per the Flyer book. The last 5' of hose going to the filter/ reservoir was the 5/8" ID. A friend tells me that tractors use the same size hose for both lines. So, I'm still confused about why that piece of 5/8 hose was in there. I called the New Flyer company some time ago about something different and they didn't know anything about the old coaches.

I also wonder if the pump just recirculates the fluid until the steering wheel is turned or if the supply line has pressure and none on the return line until the wheel is turned? Sometimes I think to much about things. Jim

OneLapper · December 29, 2008, 04:37:27 PM

Your power steering system is an "open center" system that always circulates fluid. The fluid it then diverted by whatever type of steering control you have (steering boosting cylinder, power steering gear box, etc).

Mark

Sojourner · December 29, 2008, 06:44:43 PM

About the return PS line from power steering unit to filter unit....it is not a high pressure line but fluid return line. PS's filter is either within reservoir/filler unit or in-line filter.

About the size of line...it the flow restriction that matter, not pressure but head-pressure at the power steering gear box's outlet (return). The lower the head-pressure the better. However, being 35ft or so and ½ inch ID should be minimal head pressure during very cold climate. No need to use 5/8 inch ID for 5ft.

FWIW

Sojourn for Christ, Gerald

JohnEd · December 29, 2008, 07:37:53 PM

I recently replaced the hi pressure flex PS hose on my car. The rubber hose turned into metal tubing before the servo and it also looped back on itself for three feet. Turns out that the metal is a heat exchanger. I have had other vehicles that had a tiny finned radiator mtd on the pump to cool the fluid. You "used to" have metal pipe running a total of 70 feet(or so). Think the engineers might have factored in "fluid heat loss" to the design using metal pipe? Counter point: it is easier to move properly heated oil through a system than cold oil so REGULATING THE TEMP would be the ideal system.

That "rusty iron pipe" isn't iron...betcha. Galvanized iron pipe has a pretty low working pressure. "Black iron pipe", as used for gas installation, is rated for 2,000 PSI I was told and it is STEELE PIPE.

You want the return pipe to be bigger. That 5/8 th section may be part of the original design and the entire return run should be 5/8. All of my cars have follwed that logic/design criteria and you know how Detroit likes to save a buck.

If it were me I think I would leave that rusty iron pipe in place unless it was really thin.

HTH,

John

jimandsuzy · December 29, 2008, 08:04:01 PM

Your power steering system is an "open center" system that always circulates fluid. The fluid it then diverted by whatever type of steering control you have (steering boosting cylinder, power steering gear box, etc).
Mark

Mark, so there's never any (or much) pressure in the return line? And only pressure in the pressure line when the wheel is turned? Thanks, Jim