Section 3 - Basic Valve - No Controls - Emerson Daniel 700 Series Technical Manual

Technical Guide
DAN-LIQ-TG-44-rev0813
November 2013
The Introduction to Basic Hydraulics covered the subjects of pressure, force and area and how the three are combined to perform
various functions. Note the similarity between the spring loaded hydraulic cylinder in Figures 2-2 and 2-3 on Page 11, and the
basic control valve in Figures 3-1, 3-2, and 3-3. P1 is similar to pump pressure, P2 is similar to downstream pressure, and P3 is
similar to spring force. The Basic Control Valve uses the principles of hydraulics as described in Section 1, Introduction to Basic
Hydraulics, and performs the various control functions illustrated and described in the following pages.
The valve as shown serves no useful purpose because it does not have a pilot control loop to regulate the pressure at (P3).
The purpose of these illustrations is to show the effects and force of the main valve spring, which is the total control force of the
basic valve. All main valve springs are linear in force and are rated in psi.
The basic valve operates on a balanced piston principle and is spring biased (loaded). Since the area of the nose (P1 side) of the
main valve piston is exactly the same as the spring side (P3 side), it can be seen that the main valve spring now becomes the
differential force necessary to control the position of the main valve piston.
Three (3) different springs are applicable and selection is based on the intended service. These springs are:
Light - 4 to 6 psi force
Medium - 5 to 10 psi force
Heavy - 10 to 30 psi force
The first number given is seated force and the last is full open force.
CLOSED POSITION - The valve is closed because (P1) is less than the spring force in the seated
position or; (P2) is greater than (P1).
= Inlet Pressure
= Inlet Pressure
= Outlet Pressure
= Outlet Pressure
= Spring Force
= Spring Force
Section 3
BASIC VALVE - NO CONTROLS
Figure 3-1
12