Mokveld

shut-off valves

Mokveld axial flow shut-off valves havebeen developed over nearly fourdecades of research and fieldapplication. They combine high qualityengineering with a thoroughunderstanding of the needs of the oiland gas production, process industriesand companies involved withtransmission, distribution and storageof fluids.

Axial flow valves were originallydesigned for hydro power plants,where they have been in use since thebeginning of this century.Mokveld adopted the unique advantagesof the axial flow principle in 1955 andhas taken the lead in development ofthe axial design for valves used in theoil and gas industries.

Mokveld axial flow shut-off valveshave found worldwide acceptanceacross a large range of gas and liquidapplications: production, treatment,transmission, storage and distribution.Fluids handled range from crude oil torefined products, from high GORmultiphase fluids to heavily sandloaded natural gas.

Mokveld has supplied shut-off valvesto the world’s largest oil and gasproduction facilities, gas storagefacilities, and gas transmission systems.

Mokveld shut-off valves axial flow, a unique concept that works

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HIPPS valve 24” ANSI 900 lbs for gaslanding station at Zeebrugge Belgium

HIPPS valve 16” ANSI 1500 lbsin German compressor station

The Mokveld axial flow shut-off valve isa rugged, low maintenance, highperformance valve, providing efficientservice over a long period in a range ofmany applications.

bubble tight shut-off

Even under the most severe workingconditions, Mokveld shut-off valvesmaintain tight shut-off over the fullpressure range. Mokveld’s uniquesealing system has a proven record forreliability in applications where shut-offvalves are required to provide bubbletight shut-off after extended periods ofoperation. The main seal is protectedfrom the high velocity flow.

suitability for throttling applications

The Mokveld shut-off valve is designedfor throttling service. The throttling iscontrolled by steel parts in the valveseparate from the main seal and seat.

pressure balanced

The design of the Mokveld shut-offvalve includes a pressure balancedpiston eliminating pressure differentialsacross the piston. This significantlyreduces the thrust to be overcomeby the actuator and limits wear on themoving parts. Stroke times aresubsequently very fast, with smalleractuators and a low mass of movingparts in the valve. Fast stroke times areessential for over pressure protectionsystems (HIPPS) and emergencyshutdown applications.

high integrity pressure protection

systems

The fast acting pressure balancedMokveld shut-off valve, RZD-X-SAV,is ideally suited for over pressureprotection systems (HIPPS).Independent of valve size and rating,response times can be 2 seconds orfaster. The main sealing integrity ismaintained by a design which protectsthe seal and seat from flow damage.

The valve and actuator and instrumentdesign meet stringent safetyrequirements for HIPPS applications.

bi-directional flow and sealing

The valve design allows flow in bothdirections. Bubble tight sealingis provided with pressure up ordownstream of the valve.

fire safe design

Mokveld shut-off valves can be certifiedfire safe according to API 6FA.

complete range of sizes and pressure

ratings

Shut-off valves are available in allsizes up to 48” and pressure ratingsfrom ANSI 150 to ANSI 2,500, and upto API 10,000.

the shut-off valve that offers more

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The piston is operated by means of a90 degree angle transmission consistingof a pair of sliding tooth racks withmatching teeth located on both pistonrod and stem. Small tolerances on thegear teeth ensure that the Mokveldgearing is hysteresis free with no ‘play’between valve stem and piston rod.The flat tooth beds are isolated fromthe fluid by double primary seals on thepiston rod and guide.

Axial flow refers to the straight linesymmetrical and unrestricted flow pathbetween the valve inner and outerbodies. Major components of theMokveld axial flow shut-off valve arevalve outer body (1), inner body (2),piston (3), piston rod (4) and valve stem(5) and seat (6). The valve body is a single piece steelcasting. The wide body concept providesvery high capacities with overallpressure losses kept to a minimum.

axial flow

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stem•

piston rod

piston•

valve in closed position

valve in open position

1________________•

5_________________________________________________•

2 _________________________•

4___________________________•

3__________________________________________________•

6 ___________________________________________________________________________•

Under reversed flow conditions, the system works equallywell. The main seal is forced against the piston by the linepressure, effecting tight shutoff.

When the valve is open, the main seal, because of theenergizing principle, is retracted into the piston head andtherefore protected from erosion.

Mokveld shut-off valves assure bubble tight shut-off overthe full pressure range, even under the most severe workingconditions. These valves have an unsurpassed record forreliability in applications where the shut-off valve mustmaintain 100% tight shut-off capacity, even after extendedperiods of use.

The Mokveld Sealing Assembly, a self-energizing pressuredesign, consists of two high pressure rings and a springin between, all of which are located within the piston.

patented sealing system

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In the closed position pressure is applied to the internal faceof the main seal, energizing it and forcing it radially outwardsagainst the piston seat, thereby assuring bubble tight shutoff against all pressure differentials.

Note that the clearance between the valve piston and the seatis extremely small so that throttling has taken place betweenmetal faces only and to all intents the valve is closed beforethe seal is energized. Therefore the seal only completes tightshut-off and is protected from erosion. All shut-off valvesmaintain bubble tight shutoff to ANSI class VI, independentof actuation method.

Mokveld shut-off valves are pressurebalanced. This is achieved by placingline pressure both sides of the pistonand the piston rod, providing equalforces within the valve and cancellinga pressure differential.

The pressure balancing permits easyoperation, and in combination withthe low mass of the valve internals,very fast stroking speeds.

With the valve in closed position highpressure can be allowed from bothupstream and downstream sideswithout affecting the stem thrustrequired to operate the valve.

pressure balancing

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application

Pressure protection systems are required in every situationwhere risks of the process pressure exceeding the systemdesign pressure may occur. Depending on the design requirements, systems can providedifferent levels of protection; for example pressure reliefwhich is limited in practical application and usually notpreferred for environmental reasons.

design

High Integrity Pressure Protection Systems (HIPPS) areused as the highest level of defence in systems handlingcompressible fluids.

HIPPS are independent systems with a high degree ofredundancy, using highly reliable Mokveld type RZD-X-SAVshut-off valves with instruments to interrupt the passagecausing overpressure.

Overall response time of the protection system is less than2 seconds.

shut-off valve design code

Mokveld safety shut-off valves including associatedinstrumentation are designed, built and tested according tothe DIN 3381 standard, a common and widely used designcode for the HIPPS method of pressure protection.DVGW certification is available for the entire range of sizesup to 48” and ratings up to ANSI Class 2,500 lbs.

Among the regulations it is imperative that the safety deviceis of a proven reliable design. The reliability of the Mokveldsafety valve can meet the worlds most stringent safetyrequirements with references in more than 188 applicationssince 1974.

features

The design of the Mokveld shut-off valve provides featuresideally suited to the requirements of high safety standards incritical applications.

The pressure balancing system permits simple and compactspring return fail-safe actuators, manufactured and designedby Mokveld. Fast response times are further enhanced by thelow mass of the valve moving parts.

The proven and unique sealing system is protected completelyfrom the flow when the valve is full open. During throttlingthe seal and seat are both away from the high velocity flow,with energising of the seal in the last millimetres of stroke.

measuring units

Pressure switches or transmitters can be utilised for themeasuring unit. The most simple system, without anyexternal source of energy, is based on Mokveld pneumaticpressure switches. Accuracy within the DVGW/DIN standardsis AG 1 (1% deviation of the setpoint).

special application: pressure protection systems

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HIPPS valve 28” ANSI 600 lbs in natural gas booster station,Germany

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actuator

The actuator is the most important component betweenthe pressure sensing element and the over pressure controlvalve. It is specially designed for fast reliable stroking overan extended service life. Three types of Mokveld actuators are used in HIPPS service:

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Low pressure piston type, instrument air or line gas to open,spring to close.

2

High pressure (line) gas actuators. Actuator is directly drivenby the gas from the line.

3

Hydraulic piston actuator, hydraulic to open, springs toclose. This type can be supplied with two power sources:

– hydraulic supply from external source (powerpack)– hydraulic supply from a valve mounted handpump.

Mokveld actuators are designed with a multiple number ofsprings, depending on the required closing force and thenecessary over sizing dictated by DVGW and DIN standards.

materials

Mokveld has wide experience in material selection for shut-offvalves in corrosive and sweet services like crude oil, naturalgas, multi-phase fluids, potable water, produced water and seawater. Selection criteria include fluid composition, velocities,operating and design temperatures and pressures.Commonly used body materials include carbon steel,austenitic stainless steels, aluminium bronze, Incoloy 825,duplex alloys, 254 SMO, and many others.

quality control and quality assurance

Mokveld’s policy is that all valves are manufactured withinstrict quality standards. The Quality Assurance Departmenttakes full responsibility to ensure that all customerrequirements are met. Mokveld’s quality systems are in fullcompliance with ISO 9001 and API Q1 and have been auditedand approved by all major oil and gas companies, engineeringcontractors and inspection authorities.

test and inspection

Mokveld manufactures and tests its products in accordancewith standards and codes issued by API, ANSI, BS, CSA, DIN,DVGW, MSS, NACE, NS, TRbF, TRLG, and by others. In-house facilities are available for hydrostatic and gas body andseat tests. The facililties and procedures meet the requirementsas outlined in industry standards. Non-destructive testing is performed by certified ASNT-TC-1Alevel II inspectors.

general

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Computer Aided Manufacturing at Mokveld factory

API Spec 6A-0257, 6D-0270Registration Number 891209

Mokveld Valves is manufacturer of:

control valvesshut-off valvessurge relief valveschoke valvescheck valvesactuators and control systems

Separate brochures are available uponrequest.

other Mokveld products

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flowline shut-off valvesgas production plant

N/E Netherlands(by courtesy of NAM)

anti-surge control valve 12” ANSI 600compressor station, Russia

adjustable choke valves 71/16” API 10,000 with inconel cladding,

gas production field UAE

adjustable choke valves 8” ANSI 900 lbswith pneumatic actuators,gas production offshore Malaysia

surge control valves 20” and 24”ANSI 300 lbs, gas compression facility New Mexico

other Mokveld products

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pressure control valves 20” ANSI 600 lbs and safety slam shut valves16” ANSI 600 lbs, M & R station Germany

flow control valves, underground gasstorage field Germany

other Mokveld products

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safety shut-off valve 16” ANSI 600,underground storage field Germany

inline production chokes 10” ANSI 1500,FPSO Norway

flow pressure control valves and safety shut-offvalves, M & R station Germany

other Mokveld products

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shut-off valves and non-slam check valves6” ANSI 900 lbs, water injection manifoldof a crude oil production field, North Africa

Mokveld ValvesMokveld Valves bv P.O. Box 227

2800 AE Gouda HollandNijverheidsstraat 67telephone (31) 182 597500facsimile (31) 182 517977mokveld@mokveld.comwww.mokveld.com

Mokveld offices in: Houston, United States of AmericaWesel, GermanySwindon, United KingdomDubai, United Arab EmiratesSumy, UkraineBeijing, the People’s Republic of ChinaKuala Lumpur, MalaysiaStavanger, Norway

0303 Technical information and illustrations included are subject to changes without notice.