Fast Ratio Steering Box For OBS-GMT 400-Here's How I Did It Cheap

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evilunclegrimace

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this is not the flow control valve. i think you need to reread the document you posted. The picture is of the "discharge connector fitting".
I posted the incorrect article . I will try and find the correct one later. The picture that I posted IS th flow control valve, the other valve that every one is calling the flow control valve is the pressure relief vavle.
 

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1998_K1500_Sub

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I notice no one has yet cited an authority, e.g., a GM (or Ford, or Toyota) technical manual or engineering document.

Evidently "flow control valve" is what people have learned to CALL that flow sensing orifice / union / discharge connector fitting (#1 in my prior illustration)…

… and a lot of people do.

The flow control valve is a valve (#21 in the prior illustration). It moves within it's bore. It changes position. It effects a change in flow when necessary and it maintains the flow otherwise.

The orifice (#1 in the prior illustration) isn't a valve. It's a fixed device. It does not move. It generates a fluid pressure, related to the flow through its orifice, that feeds BACK to the flow control valve (#21 in the illustration) which in turn controls the flow.

The flow control valve (#21) also has a pressure function, as noted by @evilunclegrimace

If someone changes the orifice (as many do, #1 in the prior illustration), it will precipitate a change in flow. The change is due to the difference in the pressure signal the orifice (#1) sends back to the flow control valve (#21); it (#21) is the device that's controlling the flow.

The entire system requires both (#1 and #21) to work, of course.
 
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1998_K1500_Sub

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I'll volunteer some credible references, one (1) a GM Repair Manual and the other (2) a chapter from a training document used for education. In passing I'll also mention a Wikipedia entry (3). I've other references which I'll save for a later time.

Summary: The device called a "flow control valve" earlier in this thread, is not. It's known as a "pressure line union", "union" and a variety of other terms. It is not a flow control valve, although that term is often used as jargon.

The references below clarify this and related matters.

Thanks @evilunclegrimace for bringing this naming disparity to the forefront.

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References:

(1) This from the 1989 GMC Light Duty Truck Unit Repair Manual, pg. 3B3-2 POWER STEERING.

The GM manual states:

"There are two bore openings at the rear of the
pump housing. The larger opening contains the
cam ring, pressure plate, thrust plate, rotor and
vane assembly, and end plate. The smaller opening
contains the pressure line union, flow control valve,
and spring. The flow control orifice is part of the
pressure line union. The pressure relief valve inside
the flow control valve limits the pump pressure."

Figure 31 (below) is from the same document and illustrates the flow control valve (#21 in the figure) and the "fitting" (#23); this "fitting" is the pressure line union mentioned in their text above. It is also known as the "union" shown as #1 in the illustration I posted prior. Even GM's documents don't use consistent terminology for this device, although none of them mis-label it as a "flow control valve", because it's not.


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Notice how the GM manual states the "flow control orifice" is in the pressure line union. GM's "EVO" also resides there. Note that this same pressure line union is illustrated in the document once reference by @evilunclegrimace (image below, from the attached .pdf document).

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(2) The document titled Steering System Principles (link below) is evidently a training document used by the Denton, TX public school system (https://www.dentonisd.org)

The document Steering System Principles can be found here:

The training document states:

"A flow control valve, shown in Figure 8-35, is used
to control fluid flow and maximum pressure. Since all
of the fluid entering and exiting the pump is not needed
at all times of the vehicle operation, the flow control
valve
will reroute fluid back to the reservoir at higher
pump rpm to reduce fluid flow and fluid temperature."

Notice their Figure 8-35 (copied below). The "Fitting" shown there is quite obviously the same fitting I've mentioned earlier, being called a "union", "pressure line union", "pump discharge fitting" or "flow control orifice". Others in this thread have called it a "flow control valve" and included links to sales literature as evidence, but it is not.

The Flow control valve illustrated in Figure 8-35 is quite obviously the same as mentioned in the illustrations I've posted prior, as item #21.

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(3) Finally, I happened upon a Wikipedia entry for "flow control valve", which I wasn't going to cite it as it wasn't specifically written about hydraulic power steering systems and it's "crowd-sourced" information. But its opening paragraph caught my attention. It says...


"A flow control valve regulates the flow or pressure
of a fluid. Control valves normally respond to signals
generated by independent devices
such as
flow meters or temperature gauges."

So with respect to hydraulic power steering, the device that generates the signal, is the "union" / "pressure line union" / "flow control orifice". The signal it generates is in the form a pressure that's related to the flow through it.

The flow control valve then responds to the pressure signal, so as to regulate the flow.

How simple is that?


See

Flow control valve​

 

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tayto

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I notice no one has yet cited an authority, e.g., a GM (or Ford, or Toyota) technical manual or engineering document.

Evidently "flow control valve" is what people have learned to CALL that flow sensing orifice / union / discharge connector fitting (#1 in my prior illustration)…

… and a lot of people do.

The flow control valve is a valve (#21 in the prior illustration). It moves within it's bore. It changes position. It effects a change in flow when necessary and it maintains the flow otherwise.

The orifice (#1 in the prior illustration) isn't a valve. It's a fixed device. It does not move. It generates a fluid pressure, related to the flow through its orifice, that feeds BACK to the flow control valve (#21 in the illustration) which in turn controls the flow.

The flow control valve (#21) also has a pressure function, as noted by @evilunclegrimace

If someone changes the orifice (as many do, #1 in the prior illustration), it will precipitate a change in flow. The change is due to the difference in the pressure signal the orifice (#1) sends back to the flow control valve (#21); it (#21) is the device that's controlling the flow.

The entire system requires both (#1 and #21) to work, of course.
pics are from 91 gmt400 shop manual. i've also confirmed in my 86 sqaurebody and 1989 b-body manuals...
 

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1998_K1500_Sub

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pics are from 91 gmt400 shop manual. i've also confirmed in my 86 sqaurebody and 1989 b-body manuals...

Both of them simply used the term “fitting”, shown as item #73 in one image and item #23 in the other.

The “flow control valve” is consistently labeled.

Thanks for citing these mfgr technical manuals :waytogo:

My only gripe with the term “fitting” is that it makes no reference to the function it also provides, i.e., as the flow control orifice. But I’ll live with it.
 
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1998_K1500_Sub

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Referencing some other factory service manuals...

This image from a 2005 Toyota FSM, showing the flow control valve and the "pressure port union".

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From 1998 Honda Accord FSM, pg. 17-17 "Pump Overhaul". The flow control valve is shown. There's no "fitting" or "union" like on a GM pump, so the flow control orifice resides in what they've called a "sub-valve" that fits in the housing outlet.

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