[AT] Add-on hydraulics and power steering?

Tue Apr 24 00:55:10 PDT 2007

John,

You asked in your' email of last Saturday, "Can a pump be too big to run
such a system?"  The short answer is yes but I thought it would be
interesting to write down some of the trade offs that are made when deciding
pump size.

Let's take an example:
Let's say we had a Ford 8N engine on a stand and that it developed 25 HP at
2,000 RPM.
Let's say further that we wanted to use all the output of this engine to
drive a single hydraulic pump that would provide 1,500 PSI pressure when
under full load.
Question:  How big of a pump could we use without stalling the engine?

Answer: The formula for determining the HP required to drive a hydraulic
pump is:
HP = GPM * PSI / 1714 or
GPM = 1714 * HP / PSI so in this case
GPM = 1714 * 25 / 1500 or
~ 28 GPM

Now let's take another example:
Let's say we had a Ford 8N tractor with a loader and we want to determine
how big of a pump to buy.
We know we don't want to use a 28 GPM pump as that would leave no engine
power to drive the tractor when operating the loader under full load.
So, let's say we are willing to give up 25 percent of the engine power to
drive the pump which leaves ~ 19 HP to drive the tractor.

So, GPM = 1714 * (0.25 * 25) / 1500 = ~ 7 GPM

Interestingly I have three loaders that I think are all from the fifties: a
Ford, a Bush Hog and a Davis.  Two have Vickers pumps and one has a Borg.
The capacities of these old pumps range from 5 to 8 GPM at nominal tractor
speeds ... hum; maybe my 25 percent assumption was not too far off.

On a related note I finished installing the Davis loader on a Ferguson 35
last week.  The Vickers pump on the Davis was a 5 GPM pump.  I think the
Ferggy 35 has around 33 HP.  I decided I wanted a bigger pump and that the
35 has sufficient power so I installed an Eaton pump with a capacity of ~11
GPM (I have the system pressure relief valve set at 1500 PSI).

So, this 11 GPM pump, when under load, would require
HP = 11 * 1500 / 1714 or
~9 HP which leaves ~24 horses for the tractor.

So far I am pleased with this configuration (as in I like the up & down and
bucket dump speed) although I haven't yet really operated the loader in a
pile of heavy debris where tractor power - or lack of - will come into play.

I think these examples illustrate that within some broad parameters
determining pump size can be as much a matter of personal liking as it is an
exact science.

I hope this helped ... some at least.

Dudley
Snohomish, Washington

-----Original Message-----
From: at-bounces at lists.antique-tractor.com
[mailto:at-bounces at lists.antique-tractor.com]On Behalf Of Dudley Rupert
Sent: Sunday, April 22, 2007 10:09 AM
To: Antique tractor email discussion group
Subject: Re: [AT] Add-on hydraulics and power steering?

John,

The back fifteen or twenty pages of the 2004 Hydraulic Parts Components
catalogue from Force America contains a good tutorial on hydraulics.  Their
website is www.forceamerica.com and their number is 888-99FORCE.  I don't
have their latest catalogue but I would guess that it would also include
this tutorial information.

A hydraulic pump can be used for both power steering and another application
like say a loader.  However, to maintain the performance of the power
steering system while both turning and using the loader requires a Flow
Divider (or something that works like it).

A Flow Divider is like a Y valve with one input (which is connected to the
pump output) and two outputs.  One output is connected to the power steering
and the other to the loader.  The function of the Flow Divider is to ensure
that a minimum flow of hydraulic fluid is always diverted to one of its'
output ports.  Let's say power steering needs a minimum of 3 GPM to function
properly (I have no idea if this is anywhere near correct).  Then,
installing a Flow Divider with a 3 GPM rating on one of its' output ports
for the power steering could be used.  The loader, which is connected to the
other Flow Divider output port, will then only get what the pump puts out in
excess of 3 GPM.

FWIW - I have seen several tractors with power steering that used a Flow
Divider but not also with a loader - usually just a function that required a
single actuator like an add-on 3-pt hitch.  For a loader application I think
I would want dedicated pumps for both the loader and power steering, as I
wouldn't want the loader performance to suffer any while turning.

Dudley
Snohomish, Washington

-----Original Message-----
From: at-bounces at lists.antique-tractor.com
[mailto:at-bounces at lists.antique-tractor.com]On Behalf Of Larry D Goss
Sent: Sunday, April 22, 2007 7:18 AM
To: Antique tractor email discussion group
Subject: Re: [AT] Add-on hydraulics and power steering?

Are you sure the pump is turning the right way?  Some pumps have the
pressure relief valve built into them and won't run backwards.

Larry

----- Original Message -----
From: "John Wilkens" <jwilkens at eoni.com>
To: <at at lists.antique-tractor.com>
Sent: Saturday, April 21, 2007 11:15 PM
Subject: [AT] Add-on hydraulics and power steering?

> Anyone know of a good book on very basic practical application of
> hydraulics and old tractors?  One specific is...can you use a front
> or rear mount hydraulic pump that is being used to run a loader (etc)
> to run an add-on power steering unit also?  What capacity pump would
> be required?  What kind of plumbing and fixtures would be
> needed?      Also, can a pump be too big to run such a system.    I
> tried to run a wood splitter off of a large BeeGee pump hooked up to
> the belt pulley shaft on an AC WC tractor (came off of a Cat) but
> about all it did was heat up the oil and stall the tractor.  One guy
> told me the pump was "just too big."  ???
>
>                    In the wide-open spaces of NE Oregon
>
>
>
> _______________________________________________
> AT mailing list
> http://www.antique-tractor.com/mailman/listinfo/at
>

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