Home Research For Teachers HISTORY
Level 1
Level 2
Level 3
Level 1
Level 2
Level 3
Level 1
Level 2
Level 3
Search Hot Links What's New!
Gallery Feedback Admin/Tools

Please let me remind all of you--this material is copyrighted. Though partially funded by NASA, it is still a private site. Therefore, before using our materials in any form, electronic or otherwise, you need to ask permission.
There are two ways to browse the site: (1) use the search button above to find specific materials using keywords; or,
(2) go to specific headings like history, principles or careers at specific levels above and click on the button. 
Teachers may go directly to the Teachers' Guide from the For Teachers button above or site browse as in (1) and  (2).

FAQnewred.gif (906 bytes)          

Section 1.14 - Flow Control

hrule_bl.gif (260 bytes)

Selector Valves

Selector valves are used as (1) directional control devices to insure the movement of the hydraulic fluid flow in the proper direction, and (2) as stop-locks to lock the selector switch in a certain position.


There are three types of selector valves. They are rotary type, piston type and poppet type.

Rotary types

Rotary type selector valves are plugs within which are passage ways for the fluid to move through. Tubing from the hydraulic pump or return line are connected to the rest of the hydraulic system by movement of the plug. You cannot use high pressure oil because of leakage around the plug. To reduce leakage, you might want to make the plug fit more tightly into the selector valve body.  However, the better you make the fit, the more friction will exist between the plug and the selector valve body, making it difficult to operate.

hydro037.gif (662 bytes) hydro039.gif (866 bytes)

Piston Type

Positions 1, 2 and 3 (shown below) are representative positions for the piston-type selector valve. Position (1) is the position of the selector valve, for example, upon the extension of the landing gear or the lowering of flaps. Position (2) is the position of the selector valve upon retraction of the landing gear or the raising of the flaps. Position (3) is the stop-locking position of this type of valve. This piston type valve uses the Vickers spool mechanism in which the piston "lands" isolate the high pressure oil (red area) from the low pressure oil (blue area).

hydro040a.gif (5710 bytes)
hydro040b.gif (5646 bytes)
hydro040c.gif (5492 bytes)


Poppet Type - Stacked Poppet

In this type valve, any movement of the handle (at the lower right of the diagram) changes the camshaft and cam settings, thereby opening and closing the poppet valves and letting high and low pressure oil to the proper sides of the actuating cylinder and return line, respectively.

hydro041.gif (8780 bytes)

In in-line poppets, the poppet valves are set up along a cam shaft, in the same manner as for the intake and exhaust valves of a car engine. The camshaft is represented by the "sinusoidal" line in the diagram below.  However, the motion of the poppets are controlled by the pilot.

hydro042.gif (3939 bytes)

These mechanical type selector valves require a fair amount of tubing. In order to reduce the amount of tubing, electric switches have been used to operate solenoids which operate the selector valves. This has the added advantage of reducing the wasteful motions of pilot. This is type of combined electronic circuits and hydraulic system is called electrohydraulics.


Send all comments to allstar@fiu.edu
1995-2017 ALLSTAR Network. All rights reserved worldwide.

Funded in part by

Updated: March 12, 2004