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Low Flow Capacity: This could be caused by an undersized
internal valve, undersized or long downstream piping,
plugged screens, some other restriction in the
downstream system, or by the bypass valve sticking in the
open position. The bypass valve could also be set too low
and be opening prematurely.
Principle of Operation (Figure 3)
The operational schematic depicts threaded valves,
however flanged styles operate in the same manner.
Refer to the schematic drawing, Figure 3. In Figure 3, View
1, the valve is held closed by both tank pressure and the
valve's closing spring. There is no leakage past the
resilient seats in the poppet to the valve outlet in this
position.
The valve is opened by moving the operating lever to
approximately midpoint in its 70° travel (Figure 3, View 2).
This allows the cam to place the rapid equalization portion
of the valve stem in the pilot opening, permitting a larger
amount of product to bleed downstream than if the
operating lever was moved to the full open position.
When tank and downstream pressures have equalized in
the bleed position, (after a few seconds), the excess flow
spring pushes open the main poppet (Figure 3, View 3) and
the operating lever can be moved to the full open position.
If tank pressure is greater than the valve's outlet pressure,
the main poppet will remain in the closed position. If valve
outlet piping is closed off by other valves, however,
product bleeding through the pilot will increase until it
nearly equals tank pressure and the main poppet opens.
Note
The main poppet will not open if valve outlet piping is
not closed off so that the outlet pressure can approach
tank pressure.
Once the main poppet opens, a flow greater than the
valve's excess flow spring rating or a sufficient surge in
flow forces the main poppet closed against the excess flow
spring (View 4). The pilot valve allows a small amount of
product to bleed, but much less than View 2 where the
rapid equalization portion of the stem is placed in the pilot
opening. When the operating lever is moved to the closed
position, the valve closes completely and seals tightly
(View 1).
Maintenance
!CAUTION!
Do not use these internal valves if they leak, fail to work
properly, have been damaged or have missing parts.
Prompt repairs should be made by a properly trained
serviceman. Continued use without repair can create a
hazardous situation which could result in serious or fatal
personal injury or property damage.
A simple preventative maintenance program for the valve
and its controls will eliminate many potential problems.
Form #995 ME990S-2F-16 & ME990S-2DFM IOM
ME990S-2F-16 and ME990S-2DFM
MEC recommends these steps be conducted
once a month. Also refer to the Department of
Transportation (DOT) CFR 49 Sections 180.416 and 180
Appendix A and B which specify monthly maintenance
and inspection tests for cargo tank service internal valves
and their actuation controls.
1.
2.
3.
4.
5.
Parts Ordering
Use only genuine MEC replacement parts. Components
that are not supplied by MEC should not, under any
circumstances, be used in any MEC valve, because they
might adversely affect the performance of the valve, and
could give rise to personal injury and property damage.
When corresponding about this equipment, always
reference the equipment model or series number found
on the nameplate.
SRK – Seal Repair Kit
VRK – Valve Repair Kit
PGA – Packing Gland Assembly
PRK – Packing Repair Kit
See parts list for corresponding parts and service kit
components.
Inspect the operating lever to see that it operates
freely and that there is no leakage around the
retainer nut. If there is sticking or leakage, replace the
packing and bushings. Refer to parts list.
Check for tight closure of the seat discs. Any detected
leakage, which is normally caused by disc wear, dirt,
scale or debris embedded in the disc, requires that
the internal valve be removed from service and
repaired. Repair most often requires the replacement
of valve discs. To check for leakage:
a.
Close the internal valve and exhaust downstream
pressure. Close the first valve downstream from
the internal valve and note any pressure build-up
using a pressure gauge, between the closed valve
and the internal valve. If piping is cold allow it to
warm to ambient temperature.
b.
Refer to CFR 49 Section 180 Appendix B for Meter
Creep Test Methods.
All operating controls should be inspected, cleaned
and oiled. The controls should be checked to see that
they fully open but not over travel the internal valve
operating lever and operate freely to close the valve.
Standard construction internal valves must be
removed if the container is to be steam cleaned. Heat
can damage the valve's seats and seals.
Standard construction internal valves are not
designed for water service. Immediately after a
container is hydrostatically tested, remove all water
and allow the container to thoroughly dry out.
Important
Valve
ME990S-2F-16
Available Service Kit
ME990S-2DFM
ME990-16-SRK
ME990-16-VRK
ME990-PGA
ME990-PRK
Rev E 2/3/21
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