When NOT to use a pump for liquid transfer.

A case study in how to transfer liquified gases (propylene, in this application) using the vapor itself.

Custom-built, explosion proof Blackmer compressor package exceeded our customers expectations!*

There are challenges when transferring liquids that are vapors at atmospheric pressures. Liquids like ammonia, butadiene, propane, propylene, refrigerants, or vinyl chloride must be contained under pressure to keep them in equilibrium. Pumps, with the limited Net Positive Suction Head available (NPSHA), cavitate and can become vapor locked.

Using Blackmer HD gas compressors to compress the vapor to transfer the product is much more efficient. Transfer faster and recover much more product with the Blackmer HD compressor.

A global chemical manufacturer (and their engineering firm) asked for “Liquid transfer of propylene from a 435 lb. cylinder to a 125 gallon storage tank and transfer from the storage tank to a feed tank”. Conditions: 20F, 57 psi inlet pressure/77 psi discharge pressure; 70F, 140 psi inlet pressure/166 discharge pressure; and 100F, 210 psi inlet pressure/230 discharge pressure thus the compressor was going to see varying conditions although the differential pressures (discharge minus suction) were pretty constant at 20 psid to 26 psid.


Using a Blackmer compressor for liquid transfer and vapor recovery

How it works:


The compressor and 4 way valve is configured to allow the destination vessel vapor to enter the compressor where the gas is slightly compressed and discharged to the top of the source container or vessel where the gas pushes on the top of the liquid forcing the liquid up the liquid line connected to the bottom of destination vessel.








When nearly all the product is transferred, you are left with a small amount (heel) at the bottom. You then change the 4 way valve and other valves to allow the vapor line from the source vessel to connect to the compressor inlet and you compress that gas and push it up through the bottom of the destination vessel. As the gas travels up through the liquid, it cools and tends to condense into liquid. This operation continues until the pressure in the source vessel drops to a pre-set point (typically dictated by economics).

The compressor transfer process described is done with many liquified gases and natural gas with the same basic process steps.

As a long-time distributor for Blackmer, we were able to provide a Blackmer gas compressor package for this important application.

Our design team assembled a complete package in our Louisville facility per the customers requirements from the ground up, including a custom steel base with forklift portability, and a complete controls package for “plug and play” installation.

* Our customer asked for 15 minute liquid transfer and we did it in about 5 minutes! 

Backside of Nema 7 control panel showing Nema 7 controls which were prewired and connected to compressor and panel.

Application details:

Liquified gas transfer of propylene from 435-gal cylinder to 125-gal storage tank and transfer from storage tank to feed tank. 4 SCFM @ 77 PSIG, 166 PSIG and 231 PSIG.

Custom compressor package:

  • Blackmer heavy-duty compressor model HD082B (Blackmer’s smallest HD size) – non-lubricated, 1-stage, vertical, air cooled, single cylinder, single acting, ductile-iron construction with packing.
  • 76”x76” structural steel baseplate with V-belt drive, belt-guard, motor slide base, liquid trap, 4-way valve and strainer.
  • 3-HP, 1750 RPM, 182T frame explosion proof motor, belt drive.
  • NEMA7 Low oil pressure switch, low suction pressure switch, high discharge pressure switch, high temp switch and SS high liquid level float switch.
  • Discharge relief valve ASME.
  • Mounted and wired NEMA 7 control panel with start/stop push button, Power “on” light, Production test report and hydrostatic test @ 503 PSIG.

Blackmer heavy-duty compressor model HD082B mounted on structural steel baseplate.


Centrifugal Pumps | An Open and Shut Case?

I am frequently asked; should the discharge valve be open or closed when the pump is started? My answer is….it depends, but regardless the suction valve better be open.

First Things First

Let’s look at the impeller. There are many things to consider, but the primary question we want to answer today is; what is the geometry of the impeller? From that shape we will determine the range of Specific Speed (NS). Ok, I may have lost you now because I used the nerdy “Specific Speed” term, but let me explain. Just for today’s purpose, let’s focus on the directional path of the liquid and specifically how it enters and exits the impeller.

Specific Speed is a predictive indicator for the shape of the curves for head, power and efficiency.

Low Ns

If the liquid enters the impeller on a path parallel with the shaft centerline and exits the impeller at an angle 90 degrees to the shaft centerline (at a right angle) then the impeller is in the low Specific Speed range. This would be a typical radial impeller like the Summit Pump model CC-FM.

Medium Ns

If the liquid enters the impeller on a path parallel with the shaft centerline and exits somewhere close to a 45 degree angle, then the impeller is in a medium Specific Speed range. These are mixed flow or Francis-Vane type impellers.

High Ns

If the liquid enters the impeller on a path parallel with the shaft centerline and exits in a path parallel to the shaft centerline, this is a high Specific Speed impeller. This axial flow type of impeller would look similar to a boat or airplane propeller.

Plan B

Don’t know the Specific Speed (Ns) of the impeller? Ask the manufacturer.

Now for the Really Interesting Part

For low Specific Speed (Ns) pumps the Brake Horse Power (BHP) required increases as you open the discharge valve and increase the flow rate, this is a direct relationship just as you would intuitively expect. For medium Ns pumps the BHP curve and its maximum point moves back to the left some nominal amount … in the past you may have not noticed this change. Axial flow pumps, of high Ns, the BHP is near its maximum point at the lower flow rates and actually reduces as the flow rate increases. Perhaps the opposite of what you would expect? Notice how the slope of the power graph also changes when the impeller design goes from low to high specific speed.

And…Answering the Original Question

I recommend that the discharge valve be closed on the startup of low Ns pumps and to be open on high Ns pumps. Note, this is a “thumb rule” and there are numerous caveats that can and will modify the answer.

  1. If the low Specific Speed (NS) pump is of any consequential size (Flow, Head and BHP) you may need to have the discharge valve slightly open to reduce the differential pressure across the valve. This step will minimize the effort to open the valve. Some pump systems will have a bypass line for this purpose.
  2. Systems that have downstream pressure (from another source) with no check valves (or check valves that are leaking by) can force the pump to spin backwards when the discharge valve is open.
  3. If you are starting a pump that will operate in parallel with another pump(s) you need to consider check valve lift points and controlling instrumentation (PID); this is a subject too cumbersome to explain in the “Sixty Seconds” platform.
  4. Normally, high Specific Speed (NS) pumps are started with the discharge valve open to reduce the electrical load and resultant stresses on the driver. In many cases the driver may not be adequately sized (on purpose) to handle the low flow power requirements and will trip offline.

-Jim Elsey




Rotary Piston Pumps

​Tuthill’s rotary piston pumps are known for being some of the most rugged, reliable equipment capable of handling especially dirty processes. Tuthill provides a 30-month warranty on all rotary piston pump models.

KT Single-Stage Rotary Piston Pump

  • High pumping capacity at high and low pressures
  • Triplex piston design: dynamically balanced and practically vibration free
  • No metal-to-metal contact between pump piston and cylinder – clearances are filled with oil
  • Quiet running

KT models include an integral, positive pressure lubrication system to insure reliable lubrication at all pressure levels. KT pumps are water-cooled. Optional air-cooling systems are available. Adjustable gas ballast valves are standard for handling water and other vapor loads.

ModelCFM / m3/hHP / kW|Typical Applications
KT-150C150 / 2557.5 / 6|Heat Treating
KT-300D300 / 51015 / 11|Coating
KT-500D500 / 85030 / 22|Transformer Drying
KT-850D778 / 132240 / 30|Metallurgy

KC and KTC Two-Stage Rotary Piston Pumps

  • Recommended for applications where operating pressure is below 0.1 Torr (0.13 mbar)
  • Achieve lowest possible pressures from mechanical pumps
  • No metal-to-metal contact between pump piston & cylinder – clearances are filled with oil
  • Unequaled durability, even in dirty applications

KC & KTC pumps are air-cooled. KTC-112 is water-cooled with optional air-cooling systems. Adjustable gas ballast valves are standard for handling water and other vapor loads. KTC pumps feature triplex piston design: dynamically balanced and practically vibration free.

ModelCFM / m3/hHP / kW|Typical Applications
KC-55 / 8.50.33 / 0.25|Evacuating Refrigeration Systems
Model CFM / m3/h HP / kW
KC-5 5 / 8.5 0.33 / 0.25
8 / 13.60.75 / 0.56|Liquid Gas Storage
KC-1515 / 25.51 / 0.75|Brake Fluid Filling
KTC-2121 / 361.5 / 1.1|Silicon Crystal Growing
KTC-6060 / 1023 / 2.2|
KTC-112107 / 1827.5 / 5.6|

KD and KDH Single-Stage Duplex Rotary Piston Pumps

  • Absolute pressures down to the low micron range
  • Belt-driven, low-speed rotary piston pumps
  • No small orifices to plug up
  • No metal-to-metal contact between pump piston and cylinder – clearances are filled with oil
  • Adjustable gas ballast permits handling of condensible vapors

KD pumps are air-cooled. KDH pumps are water-cooled.

ModelCFM / m3/hHP / kW|Typical Applications
KD-3033 / 561.5 / 1.11|Drying Chambers
KD-5052 / 882 / 1.5|De-gasifiers
KDH-130134 / 2275 / 3.7|Filling Machinery
KDH-150165 / 2807.5 / 5.6|Evacuation of Process

Liquid Ring Vacuum Pumps

Customers can choose a custom or optimized liquid ring vacuum pump from Tuthill and install with confidence it will do the job! Lean on our excellent service, support and engineering expertise.

KLRC Two-Stage

  • Can pull down as low as 4 Torr (5.3 mbar a)
  • Low-pressure performance is limited by the vapor pressure of the sealing liquid: water, oil or process liquids
  • Complete engineered system solutions available: instrumentation, controls, piping and valves
  • Self-contained liquid recovery and recirculation are available
  • Center-anchored tie rods allow access to either end of the pump without total disassembly
  • Double mechanical seals available in models KLRC75 through KLRC525 to meet API Piping Plan Requirements

Available in standard, all iron construction (no yellow metals) and 316 stainless steel. Liquid ring pumps often require water-cooling, but air-cooling systems are available.

ModelCFM / m3/hHP / kW|Typical Applications
KLRC-7570 / 1205 / 3.7|Vapor Recovery
KLRC-100100 / 1707.5 / 5.5|Deaeration
KLRC-125140/ 24010 / 7.5|Extruders
KLRC-200200 / 34015 / 11|Crystallizers
KLRC-300300 / 51025 / 18.5|Chemical Processing
KLRC-525550 / 93550 / 37|
KLRC-950950 / 1615100 / 75|

A Series Single-Stage

  • Simplistic in design, rugged in construction – handles even slugs of liquid
  • Unique axial flow design allows pump to operate flooded without damage
  • Built to run in the most severe of industrial conditions
  • Flat power curve over entire vacuum range prevents motor overload
  • No contact between operating components in the casing
  • Pull down to 29” Hg – 25 Torr (33 mbar a)
  • Increased water handling capability prevents heat build-up, extends life of single mechanical seal
  • Reduced stress on motor shaft and bearings
  • Compact, close-coupled design eliminates need for interstage manifold or motor alignment

A Series pumps are not as susceptible to cavitation compared to flat plate design because the flow path through the pump is an axial flow. This allows the velocity through the pump to be unchanged and carries the air out effortlessly. It is not unusual for these pumps to run 24/7 operation for years without maintenance.
Material of construction options include all bronze, cast iron, and stainless steel..

ModelCFM / m3/hHP / kW|Typical Applications
A-510 / 171 / 0.75|Gas Compression
A-1015 / 261.5 / 1.1|Sterilization
A-1522 / 372 / 1.5|Solvent Distillation
A-2035 / 593 / 2.2|Degasifiers
A-7575 / 1285 / 3.7|Extruders
A-100105 / 1787.5 / 5.5|Evaporators
A-130140 / 23810 / 7.5|
A-200220 / 37415 / 11|
A-300300 / 51020 / 15|

Rotary Vane Vacuum Pumps

The KVA’s simple design ensures the reliability and the durability that is required in the vacuum industry. Customers choose Tuthill for competitive pricing, local distribution and service, and superior customer service. Engineered-to-order system designs available.

KVA Single Stage

  • Most models can achieve ultimate pressure levels near 0.1 mbar (75 microns)
  • Ideally suited for clean or moderately contaminated applications when suction filters are fitted to the pump
  • Compact design for easy installation
  • Carbon composite vane material for long life
  • Oil-flooded, multi-vane vacuum pumps are single stage, air cooled and direct driven
  • Oil level sight glass and vibration isolators
  • TEFC high efficiency tri-voltage motor (208-230/460V 50/60)
  • Models KVA 25-630 include spin-on oil filter and exhaust pressure gauge
ModelCFM / m3/hHP / kW|Typical Applications
KVA-127 / 12.75 / 0.55|Vacuum Packaging
KVA-2115 / 261.0 / 0.75|Plastic Thermoforming
KVA-2521 / 362.0 / 1.5|Food Processing
KVA-4028 / 482.0 / 1.5|Central Vacuum Systems
KVA-6345 / 783.0 / 2.2|
KVA-10071 / 1205.0 / 3.7|
KVA-160124 / 2107.5 / 5.5|
KVA-250177 / 30010 / 7.5|
KVA-400300 / 50515 / 11
KVA-630460 / 78025 / 18.5|

Vacuum Boosters

Vacuum boosters are used to supercharge vacuum pumps to extend pump performance. This creates much faster pumping speeds and deeper vacuum levels. Tuthill’s vacuum boosters are designed to handle the world’s toughest applications.

  • High-capacity gas volumes at high vacuum (50 Torr to micron range)
  • May be used in conjunction with all types of vacuum pumps
  • Designed to operate at 82 dB(A) or less at blank-off (open field; motor and background noise excluded)
  • Supplied with a heavy-duty drive shaft for either direct coupled or belt-driven applications
  • Standard construction materials: cast iron housing, end plates and port fitting with ductile iron rotors and shafts
  • Special materials offered: stainless steel, carbon steel, ductile iron, Bi-Protec
  • Special testing available: Hydrostatic testing to 150 PSIG (10.35 bar g), seal leakage testing, noise testing
ModelCFM / m3/h|ModelCFM / m3/h|Typical Applications
15050-150 / 85- 255|2200860-2300 / 1461-3908|Supercharging Vacuum Systems
24070-230 / 119-391|29001130-3000 / 1920-5097|Vacuum Drying
400120-400 / 204-680|36001400-3600 / 2379-6116|Dehydration
540170-540 / 289-918|45001730-4500 / 2939-7646|Packaging
720230-720 / 391-1223|3200800-3200 / 1359-5437|Distillation
8500-850 / 459-1444|42001000-4200 / 1699-7136|Vacuum Furnace
1200400-1240 / 680-2107|54001400-5700 / 2379-9684|
1600500-1600 / 850-2718|73001800-7400 / 3058-12573|
2000650-2000 / 1104-33984000890-4000 / 1512-6796
2700850-2700 / 1444-458765001400-6400 / 2379-10874
1800680-1800 / 1155-3058|79001800-8000 / 3058-13592|
80002100-9500 / 3568-16141
100002800-10000 / 4757-16990

Dry Screw Vacuum Pumps

Dry screw vacuum pumps are environmentally friendly as there is less oil to dispose of and maintain within their design. These pumps are more efficient than a liquid sealed model and are well suited for industrial and process applications.

KDP Screw-Type Dry Vacuum Pump

  • Simple, robust design can handle process by-products – liquids, condensate, and even small particles
  • No oil or water in contact with process
  • No contact between operating components in the casing
  • Full pumping speed from atmospheric pressure down to 1 Torr; ultimate pressure 0.1 Torr (.05 Torr on Model KDP-800)
  • Quiet operation – less than 85 dB(A)
  • Short gas path through the pump for quick discharge
  • Extended shaft for either V-belt or direct drive
  • Casing and rotors made of ductile iron, PFA coated
60 Hz, Direct Drive
CFM / m3/hHP / kW|50 Hz, Direct Drive
CFM / m3/hHP / kW|Typical Applications
KDP-15088 / 1807.5 / 5.5|KDP-15071 / 1207.5 / 5.5|Solvent Recovery
KDP-330194 / 33015 / 11|KDP-330159 / 27015 / 11|Vapor Recovery
KDP-400235 / 40020 / 15|KDP-400194 / 33020 / 15|Vacuum Coating
KDP-800459 / 78030 / 22|KDP-800388 / 66030 / 22|Freeze Drying

SDV Variable Pitch, Screw-Type Dry Vacuum Pump

  • Patented variable pitch rotor design increases efficiency and lowers temperatures
  • No oil or water in contact with process gases
  • Can handle both condensible vapors and some solids without leaving residue
  • Capable of full pumping speed from atmospheric pressure to 1 Torr (1.3 mbar a)
  • Can achieve ultimate vacuum as low as 0.01 Torr (0.013 mbar a)
  • No metal-to-metal contact between operating parts
  • Complete model shown with motor and base.
  • Quiet operation

The SDV’s space saving C-face motor design eliminates the need for motor coupling and guard. It features a short gas path through the pump for quick discharge and Niflon coated internals to reduce damage from corrosive or condensate gases.

60 Hz, Direct Drive
CFM / m3/hHP / kW|50 Hz, Direct Drive
CFM / m3/hHP / kW|Typical Applications
SDV-12071 / 1205 / 3.7|SDV-12059 / 1005 / 3.7|Chemical Processing
SDV-200106 / 1805 / 3.7|SDV-20088 / 1505 / 3.7|Solvent Recovery
SDV-320188 / 32010 / 7.5|SDV-320157 / 26710 / 7.5|Crystallization
SDV-430253 / 43015 / 11SDV-430211 / 35815 / 11Distillation
SDV-800441 / 75020 / 15|SDV-800368 / 62520 / 15|Vapor Recovery

Engineered Solutions

Tuthill Vacuum & Blower Systems offers 100+ years of engineering experience and solid, hands-on care to every engineered project. Customers work directly with a project manager to develop custom solutions that efficiently meet the needs of the application. The engineering team manages the project start to finish at the Springfield, Missouri, USA facility.

Booster/Rotary Piston Vacuum Pumping Systems

  • Pump high volumes at very low pressure
  • High-capacity dry rotary lobe vacuum booster is matched to a smaller rotary piston vacuum pump
  • For continuous operation below 1 Torr (1.3 mbar a), the vacuum booster can increase pumping speed by a factor of 10 or more
  • For operation at higher pressure and for faster evacuations, the booster may be approximately twice the capacity of the piston pump
  • Performance ranges 200-12,000 CFM (340-20,388 m 3 /h) with ultimate vacuum levels as low as 0.2 microns
  • Conventional systems with direct driven or V-belt driven boosters
  • Compact systems with close-coupled boosters are available
  • Creates a higher capacity system with economy of scale

Tuthill application engineers can help you make the best selection for your specific needs.

Typical Applications
Transformer Oil Drying
Vacuum Furnaces
Vapor Coating
Vacuum Packaging

Booster/Liquid Ring Vacuum Pumping Systems

  • Ideal for pumping wet gas mixtures at low pressures
  • Oil-filled systems avoid problems with corrosive contaminants and sealant liquid vapor pressures at higher temperatures
  • Process liquid-filled systems prevent contamination of process gases with either water or oil

A variety of two and three-stage systems are available, complete with instrumentation, condensers, partial or complete sealant liquid recovery and recirculation, piping, and valves.

Typical Applications
Vapor Recovery
Chemical Processing
Dryers & Evaporators

Booster/Dry Screw Vacuum Pumping Systems

  • Combine high pumping speed with deep vacuum levels and operate free of oil, water or other sealing liquids
  • Flows range to 4,500 CFM (7646 m 3 /h) with vacuum levels to 10 microns and below

Complete engineered solutions are available and may include any combination of dry screw vacuum pumps, vacuum boosters, electric motors, direct or V-belt drive, coolant recirculation systems, instrumentation, controls, skid piping and valves.

Typical Applications
Chemical & Pharmaceutical Processing
Semiconductor Processing
Solvent Recovery
Dry Etching
Vapor Recovery

Custom Engineered Solutions

Tuthill application engineers are ready to help you select the best system and combinations of components for your specific needs. Custom engineered system solutions to 12,000 CFM are available with a combination of vacuum boosters/air ejectors and roughing pumps for any vacuum application. Contact your Tuthill rep or call 800-825-6937 for assistance.

Vacuum Pump Selector Guide

Step 1

Vertical Scale: Locate the desired vacuum level in inches of mercury (Torr or mbar*).

Step 2

Horizontal Scale: Calculate and locate the required capacity in cubic feet per minute or cubic meters per hour based on system volume, pump down time, gas load, and leakage.

Step 3

Intersection of Scales: The box where the two lines intersect contains the possible pumps for selected pressure and capacity.


*1 Torr = 1mm mercury absolute pressure

To convert inches of mercury vacuum to Torr:

Torr = (30 – inches of vacuum) x 25.4 at sea level e.g., 20 inches Hg = (30-20) x 25.4 = 254 Torr

Please consult your Tuthill sales representative for assistance in making your final product selection.

VBXpert Vacuum & Blower Sizing Tool

Gain access to the most useful tool available for blower sizing and selection! This easy-to-use interface prompts you to plug in technical specifications for your application and quickly calculates the best Tuthill product for you. Find out more at www.tuthillvacuumblower.com.

Service & Repair

The Tuthill CARE Center in Springfield, Missouri, USA is here to help with start-up assistance, repair and warranty work, and remanufactured product sales. Call 1-800-825-6937 to be connected to a Tuthill CARE technician. Tuthill has a network of authorized CARE Centers offering local service to customers. All centers are staffed with factory-trained personnel to ensure that your equipment performs to factory specifications. A listing of authorized Tuthill CARE Centers is available at www.tuthillvacuumblower.com.

Example: For 50 CFM and 80 Torr, the selector guide indicates that KD, KDH, KVA, KLRC, KDP, and SDV pumps should be considered.

Our journey of building a Conscious Company has brought us to heights where we have well-defined direction guided by our COMPASS.


Pump Testing

It shows that our client/customer base is becoming more sophisticated; because we see an increase in requests for performance tests. Testing is a great opportunity for us to exhibit our integrity and professionalism when our pumps are subsequently proven to meet the published performance data.

If the customer requires pump performance testing, the specific pump test and consequently the acceptable tolerances must be defined. The industry standard specification for our pumps is ANSI/Hydraulic institute 14.6-2011. But note, even within that 75 page specification there are numerous variables, detailed options and tolerance classes that remain to be defined.

The time to have the test, the delivery schedule and the subsequent costs defined is before the order is placed.

-Jim Elsey


Pumps are not “Plug and Play”

I repeat this message annually… no, monthly. No matter the manufacturer; the majority of all pumps do NOT come from the factory ready to start up.

The pump will require oil to be added to the bearing housings.

The impeller clearance must be determined and set for the fluid temperature. The direction of rotation should be ascertained and matched to the phase rotation on the motor driver (you must do this step with the coupling removed).

The driver will need to be aligned to the pump. When I tell people that they should align their pump nine times, I get some funny looks, but allow me to explain. Yes, the alignment may have been performed in the factory, but the very second the unit was moved for transport the alignment was lost. You will need to recheck the alignment when the unit is installed and leveled, again when the base is grouted, again after the piping is installed and again after the pump has been running up to temp.

The mechanical seal will need to be set after the above steps are completed.

Finally… please understand that most manufacturers do not install the coupling at the factory because it will just need to be removed for all the above reasons.

Be ready to complete these items, so you look like a pump professional.


-Jim Elsey