Unit# CT-4007: 2011 Stewart & Stevenson N2 Combination Pump
Listing ID: 38841 Ad Type: For Sale or Lease Contact Seller
Date Posted: October 28, 2021
Location:   Houston, TX
Condition:   Used
Contact Name:   Keith Ayers
Phone:   866-362-9817
Company:   CraneWorks, Inc.

Equipment Description:


The Stewart & Stevenson WNT-181601 combines a 180 SCFH nitrogen vaporization and pumping system with a 600 HP fluid pumping system in a trailer-mounted package. The Stewart & Stevenson non-fired nitrogen system uses the engine (glycol/water) coolant system to pass heat from the engine and hydraulic system to the liquid nitrogen using a high-pressure heat exchanger. The fluid pumping system uses a diesel engine to drive a high-pressure piston pump through a transmission.

Performance Specifications


Maximum allowable working pressure 10,000 PSI 69.0 MPa

Maximum flow rate 3,000 SCFM 85.0 standard m3/min

Maximum liquid storage 2,038 gal 7.72 m3


Pump rating 600 HP 447 kW

Pump piston diameter 3.5” 89 mm

Maximum working pressure 10,250 PSI 70.0 MPa

Maximum fluid rate 320 gal/min 1200 l/minThe combination unit consists of:

-A heavy-duty trailer

-One control cabin

-Two diesel engines

-A hydraulic system

-One triplex nitrogen pump

-Vaporizer and heat exchangers

-One nitrogen boost pump

-One nitrogen storage tank

-One automatic transmission

-One triplex fluid pump

-Fluid boost and fill centrifugal pumps

-One fluid displacement/holding tank

-High and low pressure piping

-All necessary valves and controls for normal operation

To eliminate contamination between the two systems, the fluid and nitrogen systems have separate plug valves.

Approximate Dimensions

Length 44’ 6” 13.6 m

Width 8’ 6” 2.6 m

Height 13’ 5” 4.1 m

Weight† 73,500 lbs 33,350 kg

† - Nitrogen tank empty


The trailer is a tandem axle heavy-duty twin rail trailer with the following features:

-Stewart & Stevenson design

-T1 Construction

-Single drop, twin rail

-Tandem axle (spread axle required for bridge law)

-Air ride suspension

-ABS brakes, air type

-Mud flaps

-2 speed landing legs

-Lights for highway use

-Front and rear fenders

-24 volt electrical system


The unit is fully operational from this control cabin via mechanical, hydraulic, pneumatic and electrical controls. The cabin is approximately 6’ wide x 4’ deep x 6’-10” high and is lined and fully insulated. The cabin has one side-entry locking door, sliding side window and large windows in the front and rear.

The control cabin contains all necessary controls and gauges (a portion of the following engine gauges are in the electronic display module on the panel). The cabin is climate controlled.

Standard equipment includes:

-Air conditioning and heating unit

-Heavy duty rubber insulated floor, fire resistant

-Four work lights (two at the rear and two at the front)

-Interior lights

-Work light switch

-Air pressure gauge

-Air horn button

-Battery voltage

-Fuel gauge

Each engine has a control and monitoring section in the control console featuring:

-Engine start/stop

-Emergency kill

-Engine oil pressure gauge

-Engine water temperature gauge

-Engine tachometer

-Engine diagnostic request light

-Engine diagnostic connection

-Engine throttle

The nitrogen system is controlled and monitored from a dedicated control panel. The by-pass valve and the temper valve are accessible from inside the control cabin. The nitrogen system control and monitoring panel includes:

-Valve actuator controls

-Triplex pump charge pressure

-Triplex pump hydraulic pressure

-Triplex rate and total

-GN2 discharge pressure

-GN2 temperature

-Lube pump hydraulic pressure

-Triplex pump lube oil pressure

-Triplex pump lube oil temperature

-Boost pump hydraulic pressure

-Boost pump speed control

-Boost pump discharge pressure

-Triplex pump suction pressure

-Coolant pump hydraulic pressure

-Coolant pump discharge pressure

-Coolant system temperature

-Hydraulic oil temperature

-Heat builder hydraulic pressure

-Heat builder pressure adjustment control

The fluid pumping system is controlled and monitored from a dedicated control panel. The fluid pumping system control and monitoring panel includes:

-Transmission oil pressure

-Transmission oil temperature

-Transmission shifter

-Transmission lock-up pressure

-Lock-up indicator lamp

-PTO engage switch

-Triplex fluid rate and total

-Fluid discharge pressure

-Triplex lube oil pressure

-Triplex lube oil temperature

-Centrifugal pump hydraulic pressure

-Centrifugal pump speed controls

-Valve actuator controls

-Process schematic

-Discharge valve actuator control


This unit is capable of pumping up to 180,000 SCFH of gaseous nitrogen with pressures up to 10,000 PSI and at discharge temperatures of 70?F. A hydrostatic hydraulic pump drives the cryogenic triplex pump in a closed-loop system. The front pump of a double hydraulic pump drives the water, and triplex lube pumps. The rear pump of a double hydraulic pump drives the cryogenic boost pump.

The liquid nitrogen is taken from the nitrogen storage/transport tank by a centrifugal boost pump and passed through a strainer to a high-pressure LN2 triplex pump. The Stewart & Stevenson system uses the engine (glycol/water) coolant system to pass the heat from the engine and hydraulic system to the liquid nitrogen.

The amount of heat generated by the diesel engine varies with the nitrogen discharge flow rate of this unit and the sequence valve pressure located in the closed-loop triplex pump drive circuit. Engine load increases linearly with triplex pump discharge and sequence valve pressure until the maximum load is achieved at maximum discharge rate and maximum sequence valve pressure. A nitrogen-tempering line is installed across the nitrogen heat exchangers from the liquid nitrogen input to the gaseous nitrogen output to assist in regulating the GN2 output temperature.


Installed on the deck of the unit is a Detroit Diesel Series 60, four-cycle diesel engine with a pump drive. This engine powers the hydraulic systems and has the following performance characteristics:

-Rated 600 BHP @ 2100 RPM

-Electronic engine management system

-Electronic Throttle Control

-Residential grade exhaust system with stainless steel flex connections

-Dry-type air cleaner assembly

-Air compressor system (compressor, governor, regulator/filter, dryer, and receiver)

-Fuel filtration system

-Cooling system rated for maximum ambient temperature

-Radiator fan guards

-Fuel tank

-Full flow engine lube oil filter

-Electric starting system

-Exhaust with manifold, muffler, and rain cap

-Triplex pump lube system


The nitrogen triplex pump is powered by an axial piston variable displacement swash plate-type pressure-compensated hydraulic pump. This drive system features a closed-loop hydraulic circuit for greater efficiency and superior triplex pump speed control. A high-pressure sequencing valve is installed in this closed-loop hydraulic system. This valve maintains a power load on the engine, which increases engine-generated heat for vaporization as the triplex speed is increased. The pump and motor in this circuit are oversized to produce the required load on the engine to vaporize nitrogen during high rate/low pressure pumping operations.

An auxiliary hydraulic pump system is installed on this unit to provide power for the LN2 centrifugal-type boost pump and the engine coolant centrifugal pump.

Included with the above components of the hydraulic system are the following miscellaneous hydraulic components:

-Carbon steel hydraulic reservoir tank including a pump inlet suction strainer, oil level sight glass, access hatch, baffle and in tank return filter

-Filters installed in the closed-loop main and auxiliary hydraulic systems

-Hydraulic oil heat exchangers installed with nitrogen vaporization system

-All necessary relief and check valves to prevent over pressuring and flow reversals in the hydraulic oil circuit

-Hydraulic pressure gauges, liquid filled calibrated in English and Metric units

All hoses and fittings are rated by the maximum pressure that can be generated by the hydraulic pump to which they are connected. All hoses have inner lines suitable for service with mineral oil and outer cover of synthetic rubber resistant to diesel fuel and alcohol.


This hydraulically powered triplex cryogenic pump has the following features:

-3-GUPD cryogenic triplex pump or equivalent

-Piston stroke 1.5”

-Maximum working pressure 10,000 PSI

-Mechanical type pump speed/flow rate connection

-Power-end lubrication system with reservoir, filter, and cooler

-1.625” diameter cold ends


The unit is equipped with a 1.5” x 2.5” x 6” centrifugal pump. A hydraulic motor is connected to the pump and driven by the auxiliary hydraulic system. The hydraulic circuit includes a manually controlled hydraulic valve to provide precise variation in the speed of the centrifugal pump. The pump has the following features:

-2” brass 40 mesh suction strainer prior to the LN2 centrifugal boost pump

-Rated for LN2 service

-Mechanical seals

-Manual control

-150 PSI brass relief valve

-Boost pump priming valve


The unit is equipped with a 10,000 PSI high-pressure discharge piping assembly consisting of the following:

-9/16” manually controlled bypass valve (connecting the high-pressure piping to the lower pressure piping) installed prior to the vaporizing system

-Check valve installed after the vaporizing system

-High-pressure safety relief valve set at 10,500 PSI with a vent designed to withstand the force of the vented gas

-A 2” x 1” discharge plug-type manual valve with a 2” Fig. 1502 output union for connection to the customer-supplied high-pressure discharge manifold-?9/16” manually adjustable LN2/GN2 tempering valve installed prior to the vaporizer


The unit is equipped with a low-pressure suction piping assembly. Screwed or silver brazed fittings are used and piping is type 304 or 316 stainless steel to assure safe and leak free operation.

-A brass 100 mesh suction strainer prior to the LN2 centrifugal boost pump

-A boost pump priming valve between the boost pump and the triplex pump

-A manually controlled vent-to-atmosphere valve in the suction piping assembly

-Relief valves in the low-pressure cryogenic piping wherever the possibility of trapping liquid nitrogen could occur

-1-½” hose connections for tank supply and return


An engine coolant water pump takes the coolant from the diesel engine during nitrogen pumping operations, circulate it through the nitrogen non-fired vaporization system, and return it to the diesel engine at the completion of the circuit. During nitrogen pumping operations the engine coolant radiator is by-passed by an external thermostat valve to allow maximum utilization of the engine water jacket heating systems.

However, in the event of excessively high temperature occurring in coolant fluid the thermostat system circulates the coolant through the engine radiator. This is only likely to occur at very low nitrogen pumping rates or other non-nitrogen pumping operations/procedures.

The engine coolant, at temperature ranges from 167°F (75°C) to 180°F (83°C), is then pumped directly through an engine coolant/liquid nitrogen heat exchanger to use the heat of this coolant to directly and immediately heat the liquid nitrogen.

The engine coolant is then reheated to a temperature high enough to allow the coolant to re-enter the diesel engine without causing any damage to that engine.

This coolant reheating is accomplished by passing the coolant through two hydraulic oil heat exchangers (one for each hydraulic circuit).

The amount of heat generated by the diesel engine varies with the nitrogen discharge flow rate of this unit and the sequence valve pressure in the closed-loop triplex pump drive circuit. Engine load increases linearly with triplex pump discharge and sequence valve pressure until maximum load is achieved at maximum discharge rate and maximum sequence valve pressure.

Installed across the nitrogen heat exchangers from the liquid nitrogen input to the gaseous nitrogen output is a nitrogen-tempering line to assist in regulating the GN2 output temperature at very low pumping rates.


The unit is equipped with a 2000 gallon cryogenic tank. The tank mount includes all interconnection piping and valves. The tank is equipped with a liquid level gauge assembly and a calibration chart to allow the operator to convert from tank level to tank volume. The tank has a vacuum probe valve and a thermocouple probe for checking the condition of the tank vacuum and a manifold is installed on the tank containing a tank blow-down valve.

Specifications of the tank are as follows:

LN2 Tank Specifications

Inner Shell SA-240 304 stainless steel with one transverse baffle

Outer Shell Carbon steel

Outer Shell Diameter 88"

MAWP 45 PSI (3.10 bar)

Main Safety 45 PSI (3.10 bar)

Burst Disk 1/2" disposable brass assembly set at 62 PSI

Net Working Volume 2,038 gallons (7,715 liters)

Tare Weight 5,650 lbs (2550 kg)

Insulation Multi-layered evacuated fiberglass (super insulation)

Evaporation Rate 0.8% per day

Vaporizer Aluminum fin, stainless steel pipe lined

Pressure Building unit 35 GPM @ 25 PSI LN2

Piping ASME SA-240 TP304 or 316 stainless steel

Design Codes ASME SEC VIII DIV 1

Approvals US DOT 49 CFR 178.273 (UN Tank)


A diesel engine complete with an automatic transmission drives the triplex fluid pump. The fluid triplex pump is equipped with an external reduction box.

An oil pump is mounted on the transmission to provide lube oil to the triplex pump power-end.

Two centrifugal pumps are mounted on the unit.

An open top tank is mounted next to the control cab. The open top tank allows the operator to see the inside of the tank.

This portion of the unit is operated from the control cab.


A Detroit Diesel Series 60 engine rated at 600 BHP supplies the primary pumping power to the unit. The engine drives the high-pressure triplex pump, through an Allison transmission and driveline.


The engine is equipped as follows:

- Electronic engine management system

- Lube oil pump and distribution system

- Electronic throttle control and governor

- Fuel filtration system

- Full flow engine lube oil filter

- Water circulating pump, radiator, and fan assembly

- Exhaust manifold with stainless steel flexible exhaust connection

- Muffler and rain cap

- Transmission cooler

- Cooling lines

- Fan and fan belts

- Engine lifter brackets

- Air compressor and air receiver system

- Electric start system


The cooling system is capable of cooling the engine jacket water, transmission, and down-hole pump oil, at sustained maximum power output at the rated ambient temperature.


An Allison 4700 OFS automatic transmission is installed on the rear of the diesel engine. The transmission is equipped as follows:

-Power shift (single mode)

-Fill tube and dipstick

-1800 Series output flange

-Engine mounted torque converter cooling for cooling of transmission


Installed between the transmission and pump is a heavy-duty Spicer (or equivalent) driveline assembly with heavy-duty universal joints. The installation of all drivelines is in accordance with the manufacturer’s guidelines. The driveline is equipped with a metal guard assembly complete with greasing holes.

-2-Speed 2:1 gearbox for even greater fluid pumping range


The hydraulic system is powered by a transmission-mounted PTO and includes pumps, motors, a carbon steel reservoir, control valves, and all required hoses and accessories. The hydraulic system drives:

-Boost centrifugal pump

-Fill centrifugal pump

-Lube pump

-Mixing paddle.


The following centrifugal pump system is installed on the unit:


One 3” x 4” centrifugal pump is installed as a fill pump for transferring fluid from external sources to the fluid holding tank. This pump also serves as an emergency backup pump for the boost water pump.


One 3” x 4” centrifugal pump is used to boost slurry/fluids to the triplex pumps from a fluid holding tank. This pump can also be used to supply fluid to the fluid holding tank.



A 600 HP triplex pump is mounted on the rear of the unit. The triplex pump has the following technical specifications:

-Maximum input power of 600 HP

-Forged steel monoblock fluid end with removable suction and discharge covers

-Fabricated steel suction manifold

-Fabricated steel discharge connections (2”, Fig. 1502)

-Threaded packing glands with removable stuffing box assemblies

-Hard coated plungers

-Spring-loaded plunger packing

-Replaceable alloy steel wing guided valves

-Replaceable urethane valve disc

-Replaceable alloy steel valve seats

-Bronze packing followers

-Oil pressure gauge

-4.61:1 gear ratio

-Pump half flanged drive coupling

-Crankcase breather

-Pressure lubricated crankshaft, crosshead sleeves, and wrist pin bearings

-Dry sump

The pump is suitable for pumping inhibited acids, cement slurries, sand laden fluids, and a variety of other oilwell servicing fluids. The fluid-end is valve-over-valve design.


The pump has a grease injection plunger packing lube system.

The triplex pump power-end is lubricated with a force feed filtered back flow system, driven from the engine lube system PTO’s.


One set of pump maintenance tools to include:

-One impact hex wrench

-One slide hammer tool

-One packing wrench

Note: The pump does not require a tee wrench or a valve spring depressor.


A single-compartment fluid displacement tank is mounted on the unit beside the operator cabin and has the following specifications:

-10 BBL capacity

-Open top

-Enumerated barrel marker in half bbl increments

-Mixing paddle in tub

-Carbon steel construction


-Discharge – single high-pressure 2” 1502 treating line

-Release line – Two 2” x 1” plug valves leading to a 1” release line


The above unit shall be fully assembled, unitized and completed to Stewart & Stevenson’s specifications:

This shall include the following items (if these items are already detailed above, they shall not be duplicated):

-Decking on the unit

-Installation of lights for 24 hour use

-Installation of all other electrical systems

-Installation of all pneumatic systems

-Installation of all hydraulic systems

-Installation of all necessary hose racks as per available space

-Supply of all operating oils, coolants and other operating fluids

-All steel and miscellaneous fittings to complete the unit

-All labor to complete the unit

-General workmanship will be of good quality and appearance with the following listing a number of standards adhered to by Stewart & Stevenson:

o Flame cut edges shall be ground smooth

o Sharp corners and edges to which operators and mechanics are vulnerable shall be ground smooth

o Bolt holes shall be drilled or precision cut (laser, plasma, etc.) and sized according to Stewart & Stevenson engineering standards

o Welds shall be of good quality and of sufficient strength

o Use self-locking nuts where applicable

o All hoses will be well supported with support type clamps

o No sweated or brazed type hydraulic fittings will be used

o All hydraulic hose assemblies will have swivel ends

o All hoses will be protected by well-secured rubber sleeves to prevent rubbing by frame, etc.

o Hydraulic reservoir to be constructed plate with sight level gauge, cleanouts, vent, fill cap, etc. o The priming and painting of the equipment as per Stewart & Stevenson’s standard paint specifications

o Level 1 – Urethane Paint System

- The complete testing of the equipment at the Stewart & Stevenson, plant in Houston, Texas, USA.

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