Hydraulic Brake System - questions about valves
 

Hi,

I'm looking for detailed description about PRESSURE REDUCING VALVE and MODULATING VALVE. Especially how it's works. I've been looking in maintenance manuals from EMB170 and B733, but I could not find it. What is the difference between #1 and #2 valve? Attached figure can be found here:

https://www.dropbox.com/s/noufdk0hc8...stion.bmp?dl=0

Kind regards
Jacek

Sorry mate I am a bus boy, however looking at the pics it seems the pressure reducing valve does what it says on the tin.. pressure goes in and as it goes up it acts against the piston which in turn presses against the spring. If the pressure goes above the balancing force of the spring it uncovers more of the return port returning the excess fluid thereby keeping pressure to the lower port at a constant value. If the inlet pressure goes down then the piston moves down with spring pressure covering the return port and keeping the outlet pressure modulated to a nominated value. As marked valve 1 and 2 look the same.


The Modulating valve I guess is trying to keep a constant pressure to the brake unit with varying flow (probably for the antiskid valve at the return?) Bus brakes don't have such items in them.


Hopefully a brand B expert has the full answer for you.

Hi everyone, Hi 320busboy,

Thank you for your message.
1) Regarding PRESSURE REDUCING VALVE. I'm wondering if there is a mistake in the figure, or everything is fine. My general question about this valve is: At which port the orifice should be. At the return one, (fig #1), or at the inlet (fig #2)

2) Regarding MODULATING VALVE. I found a system schematic manual from b733, and I think that this type of valve is present. I marked it by red arrows here:
https://www.dropbox.com/s/bqwl5tag98sd7th/b737.bmp?dl=0
, but I didn't find any name of it, or details about it in AMM. Do anyone know where to search for it?

Kind regards,
Jacek

These diagrams are showing a cross-section of a typical valve and maybe different models, doing a similar function.

1/ Looks as though the pressure required to the brake is stable, so fig 1 is bleeding some pressure back to return.

2/ Pressure to the brake is low, spring pushes spindle down so the return port is covered until the supply pressure builds up again and equals the spring pressure then uncovering the return port as shown in fig 1

Today, AMM's will not normally give such fine details of the internal workings of any component. This manual is for removal, installation and testing as is required.

Component Maintenance Manuals (CMM) will give a better view of the inner workings of these valves but you will need to know the manufacturers name, eg Parker etc. You will also need to understand hydraulic principles to make these components work in your mind.

TW