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Subsea Engineer s Handbook Section 10

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Table Of ContentsSection 10

Page

1. Gate Valve Operation 1

2. Cameron Type F Gate Valve 2

3. Cameron Type AF Subsea Gate Valve 3

4. Cameron Model DF Valve 4

5. Cameron Model MCS Valve 5

6. McEvoy Valve 6

7. WOM Valve 6

8. Typical Valve Problems 9

9. Gate valve Operational and Inspection Points 9

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1) Gate Valve Operation

a) Used in choke and kill manifolds and on ram outlets to control flow up the riser

mounted choke & kill lines through the manifold.

b) Gate valves close the flow of wellbore fluid with a gate sliding across the valvesbore similar to the operation of a guillotine.

c) Most gate vales used for mud service use a solid gate which floats downstreamto form a metal-to-metal seal against the valves down stream seat. With thisconstruction the valve cavity contains full wellbore pressure when closed.

d) The WOM magnum seat forms both a downstream and an upstream seal1,simultaneously.

e) McEvoy valves employ the floating gate concept but use a unique seat design.

The valves use a gate-to-seat sealing mechanism with a sealant injection toactually create the seal between the two. Wellbore pressure acting on a piston inthe downstream seat forces the sealant into the groove between the closed gateand seat.

f) Hydraulic operators use 1,500 psi for normal operation but up to 3,000 psi maytypically be applied since most operating chambers are rated for this pressure.

g) Subsea ram outlet valves are spring loaded into the closed position. They must

be hydraulically pumped into the open position. LMRP test valves have areversed gate installed to make them spring loaded into the normally openposition. They must be hydraulically pumped into the closed position.

h) Typically, as a balanced subsea valve closes if the pressure across the gate isgreater than 500 psi, the valve will not close with only spring action. Hydraulicpressure will usually be required.2

i) Accumulated closing assist pressure typically found on Cameron controlsystem. Closing pressure applied only when opening pressure is shut off

1Currently the WOM Magnum is the only mud service valve with a solid gate which forms an upstream

and downstream seal.2A balanced valve has a tail rod or balance rod attached tothe gate. The actual pressure for the valve

will depend upon the valve manufactures design.

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2) Cameron Type F Manual Gate Valve

1. Gate and seat 2. Bonnet3. Seat retainer plate 4. Needle thrust bearings5. Stem packing retainer 6. Back seat shoulder 7. Stem Packing weep hole 8. Valve cavity HP grease fitting

3) Operation of Manual Gate Valves

a) After closing a manual gate valve the handwheel should be backed off 1/8th to1/4thturn to allow the gate to float in the valve cavity.

b) When opening the valve the handwheel again should be backed off or the gate,over time, can jam up against the bonnet.

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4) Cameron Type AF Subsea Gate Valve

The AF valve is wellbore pressure assist close. With a 7 to 1 opening ration and 10,000psi wellbore pressure in the valve, an opening pressure of 1,428 psi is required to holdthe valve in the open position.

Note: The vent port from the enclosed tail rod area connecting to the valves bore.

This port must not be oriented to the line between valves in a dual installation. Thediagram below shows the correct installation.

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5) Cameron Model DF Valve

With the tail rod attached to the gate, the DF valve is balanced. Wellbore pressure doesnot attempt to close the valve. For this reason a hydraulic assist circuit is usuallyprovided by Cameron to ensure that the vale returns to the closed position

Accumulator bottle circuit, Cameron Engineering Bulletin #707C

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6) Cameron MCS Valve

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7) McEvoy Valve

a) Seat sealant injection mechanism

Note: When pumping sealant into the downstream reservoir, the seat must be held

against the downstream seat with wellbore pressure of around 500 psi in order to ensure

that the sealant is forced into the reservoir and not allowed to pass between the seatand gate. When the reservoir is filled, the sealant injection pressure will abruptly riseseveral thousand psi as the reservoir piston hits the valve bonnet.

8) WOM Valve

a. Used on ram outlets to control flow up the riser mounted choke & kill lines

b. Steel gate acts as a guillotine to cut off flow. Gate seals against a seat forming anup-stream anddown-stream seal, simultaneously.

c. The WOM Magnum is one exception to the floating gate design. With its pressureenergized seats, the metal to metal Magnum seats form a seal on both theupstream and downstream seats simultaneously.

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d. If both seats are sealing properly there will be no wellbore pressure in the valvecavity when the valve is closed.3

e. Hydraulic operators use 1,500 psi for normal operation but operating chambersare rated for 3,000 psi WP

f. Spring loaded into the closed position and hydraulically pumped open

g. The 10,000 and 15,000 psi WP valves are provided with a balance stem (tail rod).

h. In deepwater applications all valves use hydraulic pressure to not only open but toassist the spring in closing the valves.

i. Hydraulic closing pressure is accumulated in stack mounted bottles to assist the

spring in closing the valve.

3This is true when the valve is closed prior to pressure testing. Then test pressure is applied to a fully

closed valve.

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WOM Valve Assembly

WOM Valve Operator Assembly

Open EndedCylinderEasy replacementof piston seals

EncapsulatedSpringRemains infactor assembl

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9) Typical Valve Problems:

a) Seat to gate seal not holding wellbore pressure

b) Stem or tail rod packing not holding wellbore pressurec) Bonnet seal/ring gasket not holding wellbore pressured) Spring not returning valve to the closed position when opening hydraulic

pressure is released.

10) Gate Valve Operational and Inspection Points

a) All Valves

i) After closing a manual gate valve the handwheel should be backed off 1/8 to1/4 turn to allow the gate to float in the valve cavity. When opening the valve

the handwheel again should be backed off or the gate can jam against thebonnet.

ii) The #1 maintenance item grease the valve after every pressure test. Thatwill reduce your maintenance work dramatically. Ensure that themanufactures recommended grease (or its equivalent) is used.

iii) When performing surface pressure testing between wells, pump the valvesopen and allow only the closing mechanism to close the valves. This is tocheck the fail-safe operation of the valve with no wellbore pressure applied.

iv) Periodically remove the targeted blind flanges on the stack outlets and thechoke manifold to ensure that the lead is properly in place.

v) When assembling a hydraulically operated gate valve the position of the gateon the seat (called timing) must be adjusted. This allows the hole in the gateto line up with the hole in the seat when the valve is in the open position.

b) McEvoy Valves

i) The McEvoy valve is very reliable, only when the sealant reservoir is filledproperly. To fill the reservoir requires a special technique. Simply pumping

sealant into the vale when in the closed position (as per McEvoy instructions)and waiting for a pressure rise indicating that the reservoir is filled, may notbe sufficient. Sealant may flow into the valve cavity, not into the sealantreservoir. This will cause the valve to hold pressure for only a few closuresbefore running out of sealant and beginning to leak again (possibly with thestack back on bottom).

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ii) To ensure that sealant is pumped into the sealant reservoir and not the valvecavity, apply 500 psi wellbore pressure to the closed valve and pump sealantinto the downstream seat. The pressure will force the gate onto the seat

ensuring that the sealant must travel up into the reservoir as desired. Theprocedure must be repeated for the valves opposite seat.

iii) Due to the split gate design, the McEvoy valve is capable of trapping pressurein the valve cavity when the valve is in the fully open position. Caution mustbe exercised when performing maintenance on this valve.

c) WOM Valves

i) The WOM Magnum conversion is one exception to the floating gate design.With its pressure energized seats, the metal to metal Magnum seats form a

seal on both the upstream and downstream seats simultaneously.

ii) If both seats are sealing properly there will be no wellbore pressure in thevalve cavity when the valve is closed.4

4This is true when the valve is closed prior to pressure testing and than the test pressure is applied to a

fully closed valve.