Stand Alone Pressure Motive Pump

Stand-Alone Pressure Motive Pumps (PMPs)

Pressure Motive Pumps (PMPs) are pressure driven pumps which return condensate back to the boiler room; normally using steam pressure as the motive force. PMPs can be supplied as individual pump units – which include a pump tank, the internal pump mechanism, and a set of inlet and outlet check valves – or as a packaged system which also includes the vented receiver mounted on a common base.

A separate vented receiver is required for the Pressure Motive Pump (PMPs) to operate. The vented receiver collects and temporarily stores the condensate during the PMPs’ discharge cycle when the pump tank is pressured with steam. (See purpose of vented receiver)

Ductile Iron

Significantly more corrosionresistant to condensate when compared to carbon steel.

Ductile Iron or Stainless Steel

For lower capacity applications.

Fabricated Carbon Steel

Carbon Steel may be required by code in Chemical and Petro-Chemical industries (required in certain industries).

304L Stainless Steel
(Corrosion Resistant)

Can serve as a substitute for fabricated carbon steel tanks for extended life or when Stainless Steel is required.

Carbon Steel

For applications requiring large transfer rates of condensate or other liquids.

What is the purpose of a Vented Receiver

The condensate return piping is connected to the inlet of the vented receiver to initially collect the condensate prior to the pump. The receiver tank will temporarily store the condensate during the PMPs’ discharge cycle when the pump tank is pressurized with steam. Condensate flows by gravity from the vented receiver to the pump and is then returned back to the boiler room. The receiver and vent must be adequately sized to allow for proper flash steam separation without building up pressure inside the receiver. Higher condensate pressures and temperatures, or higher condensate loads require larger receiver and vent sizes. By connecting the condensate return line to a vented receiver, the pressure in the return line will be effectively equalized to atmospheric pressure, allowing condensate to freely drain from all condensate sources. This is an extremely important and often overlooked aspect of any properly operating steam and condensate return system.

PMPs with a Vented Receiver (Complete Package Systems)

As an option to a Stand-Alone PMP pump, Watson McDaniel offers Complete Packaged Skid Systems (Simplex, Duplex, & Triplex) which include stand-alone PMPs with check valves and a vented receiver mounted on a common base. Duplex & Triplex systems can be used for increased capacity or in the event of a single pump failure. All components of the system are properly sized and pre-piped together; requiring only four connections to be made in the field. (see Complete Packaged Skid Systems)

Installation of a Pressure Motive Pump (PMP)

The installation of a PMP pump requires the use of a vented receiver to collect the condensate. The receiver must be properly sized to store condensate during the discharge cycle of the pump and to neutralize condensate pressure through a properly sized vent to atmosphere. This maintains a 0 PSIG in the receiver tank to assure that condensate will freely flow by gravity to the receiver tank and then to the pump tank, avoiding potential condensate back up. For optimum performance, it is recommended that the motive pressure should be no more than 20 psig higher than the condensate back pressure.


Condensate first enters the vented receiver. Both the receiver size and vent pipe size must be large enough to vent the flash steam created by the hot condensate without building up pressure. The receiver also serves to temporarily store condensate during the discharge cycle of the pump; when the pump tank is pressurized with steam.
Fill head is determined by the distance from the top of the pump to the bottom of the receiver tank. Increasing fill head will increase pump capacity. Standard fill head is 12 inches.
Motive pressure for pumping condensate should be approximately 20 PSI higher than condensate back pressure. A PRV may be installed to reduce motive pressure to the pump.
Condensate back pressure including vertical lift if any.

Simplify Installation with a Complete Packaged System

Complete Packaged System (Simplex, Duplex & Triplex) are offered with PMPC, PMPF & PMPNT pumps along with a Vented Receiver mounted on a common base. Packaged Systems ensure that all components and ports are sized correctly, and that installation will be simplified with only four connections to be made in the field. Multiple PMP pumps can be used for increased capacity or for system redundancy.

Simplex Packaged Pump System
Single PMP pump with receiver tank mounted on a common base.

How Pressure Motive Pumps (PMPs) Work

PMPs use steam pressure to pump the hot condensate that drains from the vented receiver tank into the PMP pump tank. The PMP pump tank cannot be used as the vented receiver since it is intermittently pressurized with steam to pump the condensate. PMPs require a separate vented receiver to collect the condensate and to vent the flash steam to atmosphere. The Simplex, Duplex or Triplex packaged systems include the separate vented receiver tank mounted on a common base along with the PMP(s).

A Vented Receiver (or Flash Tank) is used to collect the condensate generated from one or several different sources (drip & process applications) in the facility. Pressure from the Flash steam generated by the hot condensate is vented to the atmosphere to maintain atmospheric pressure (0 PSIG) in the receiver tank. This assures that condensate will freely flow by gravity to the receiver tank and then to the pump tank, avoiding potential condensate back-up.

The Internal Working Mechanism

The heart of the PMP is the internal working mechanism, which features the Pantented SNAP-ASSURE TM Design. This feature, exclusive to Watson McDaniel’s PMPs, Guarantees to extend pump life even in the most demanding applications.

The environment inside a pump tank can be extremely harsh and volatile. Hot condensate can be very aggressive and may even corrode stainless steel springs when they are under tension or compression (high stress). This is known as stress corrosion-cracking. Additionally, condensate systems normally contain fine particles of rust and other contaminants, such as pipe scale, further aggravating mechanical components. The Watson McDaniel Pump Mechanism has been refined and developed over many years and has proven itself in its performance and reliability.

Operation of PMP Pressure Motive Pump

Condensate flows from the receiver tank through the inlet check valve and fills the pump tank. During the filling cycle the float inside the tank rises.

When the pump tank has filled to the trip point, the mechanism triggers, opening the motive gas inlet valve and simultaneously closing the vent valve. This allows motive pressure to enter the pump body, which drives the condensate thru the outlet check valve into the condensate return line. During the discharge cycle, the liquid level and the float inside the pump tank drop.

At the lower trip point, the mechanism triggers and the motive gas inlet valve to the pump tank closes and simultaneously the vent valve opens. The fill and discharge cycle then repeats.

How To Size

The Capacity charts cover both stand alone pumps (PMPC, PMPF, PMPLS, etc.) as well as Pumps with Receiver Tanks (Simplex, Duplex, Triplex). If a stand alone pump is chosen, consideration should be given to the size of the vented receiver that collects the condensate before the PMP (see flash tank vent sizing). If the pump is replacing an existing installation, a vented receiver that is acceptable in size and configuration may already be installed. If required to meet capacity, pre-packaged systems with more than one pump, such as the Duplex or Triplex are available. These units come premounted with the pumps (s), a receiver tank as well as other options to optimize the system. A multiple pump unit may also be chosen for reserve capacity or pump redundancy in critical applications.

Sizing and Selecting a PMP

To select the proper size pressure motive pump requires you to know a few key pieces of information:

Condensate load you need to pump: Condensate Load is normally expressed in lbs/hr. To convert the GPM flow rate, note that 500 lbs/hr is equivalent to 1 GPM.
Motive Pressure: The motive pressure of the steam (or other gas) impacts pump capacity. The sizing chart indicates different flow rates based upon motive steam inlet pressure. It is recommended to regulate the steam inlet pressure to 20 PSI above the total back pressure.
Fill Head: Is the height (in inches) of the condensate receiver tank (or flash tank) above the pump tank. This head pressure determines how quickly the pump tank will refill with condensate after its discharge cycle. Therefore, reducing the fill time will increase the overall capacity of the pump. The capacity chart is based on 12” of fill head (PMPLS based on 6” fill head). Increasing fill head height can increase capacity by as much as 20 - 50% (See Capacity Correction Chart.)
Back Pressure: Back Pressure is the sum total of condensate return line pressure and the physical height that the condensate needs to be elevated. (See sizing section for guidance on how to calculate back pressure.)


Inlet x Outlet Size:
In addition to body material, pumps are designated by inlet and outlet size. For example, PMPC 3 x 2 has 3” inlet and 2” outlet check valves with a ductile iron tank. Since the pump fills by gravity from teh receiver tank located above it, the size of the inlet check valve significantly impacts pump capacity. The larger the check valve, the quicker the condensate will fill the pump tank, allowing it to cycle again. For example, a 3” check valve may have twice the inlet flow rate of a 2” check valve. The size of the outlet (or discharge) check valve also affects capacity but to a lesser extent.

Capacity Charts

The PMPC pressure motive pump body & cover are manufactured from ductile iron. ASME “UM” code stamp is available. This pump is typically used when liquids must be moved to higher elevation, higher pressure or extended distances.                                                                   

The PMPNT is a low-profile pressure motive pump used for applications requiring compact design due to spatial constraints. This pump is typically used when liquids must be moved to higher elevation, higher pressure or extended distances. Includes: Body, Cover, Internal mechanism and Check valves. The tank body is available in ductile iron or stainless steel.

The PMPF / PMPSS pressure motive pump body & cover are manufactured from Carbon Steel / Stainless Steel. These tanks are fabricated with 1/8” corrosion allowance and receive the ASME “UM” code stamp. This pump is typically used when liquids must be moved to higher elevation,higher pressure or extended distances.

The PMPBP is an extremely high-capacity pressure motive pump for applications requiring large transfer of condensate or other liquids. The internal operating mechanism functions identically to other pumps in the PMP series. ASME “U” code stamp is available.