www.energyabsorption.com
Revision B December 2013
www.highwayguardrail.com
32
All rights in copyright reserved
Check Valves
1.
The Purpose of a Check Valve is to Allow Free Flow in one Direction but Block
Reverse Flow.
2.
Two Types of Check Valves are Used:
A. Ball type
B. Poppet type
3.
Styles of Check valves Used:
A.
Internal style
In an ''internal'' style, a cavity is drilled in the pump base into which the parts are
assembled (inside pipe port cavity).
B. External style
A check valve mounted ''outside'' the pump base in a housing of some type is called
an external check valve (in line). The housing is usually hex-shaped.
Note:
Both styles of check valves use either types of construction depending on
application and model.
4.
Troubleshooting and Repairing Check Valve Failures.
A. Load drift failure.
1. Symptom: in
most cases a check valve will fail such that a load will drift down
when the unit is in the ''hold'' position.
Note:
Check cylinder for leakage past piston seals (See cylinder section). A bad piston
seal will give the same symptom.
2. Repair procedure.
a.
Remove the Spring Retainer.
Note:
Measure the depth to the Spring Retainer so it can be re-assembled to the same
depth after repair.
a. Remove spring.
b. Remove ball or poppet.
c. Start pump to ''flush'' dirt from the seat area. (Caution: use hand or a piece of
hose to divert oil into a container - do not look into the port).
d. Inspect ball or poppet for damage and replace if necessary.
e. Re-assemble ball or poppet.
f. ''Seat'' the ball or poppet using a small drift punch and hammer with a light
tap.
g. Re-assemble the spring.
h. Replace the
Spring Retainer to the correct
depth.
B. Blocked flow failure.
1. Symptom
a. Once in a while a ball type check valve will restrict flow to the point where the
spring will collapse and the flow will be greatly reduced (even blocked)
causing flow over the relief.
1. Repair procedure
a. Remove the check valve components and replace the spring.
b. If the problem persists replace the ball type with a poppet type as they cannot
completely block flow.
Note:
Do not use Teflon
®
tape on hydraulic fittings as it can easily clog valves and plug
the filters in the system.
