Patent Application
20080260551
The invention relates to a pump and product delivery. More particularly, the invention relates to rolling diaphragm type pumps.
In a rolling diaphragm type pump, a small amount of positive differential pressure is needed to keep the diaphragm in the correct orientation (convoluted orientation). However, if the differential pressure is too high, the diaphragm will wear out at a faster rate or even burst in extreme cases.
Prior art rolling diaphragm pump designs create a positive differential pressure by sizing the driving cylinders to match the diaphragm diameter. This limits the diaphragm size to one that will match with commercial cylinders. Additionally, the greater the mismatch, the more the differential pressure will vary with the pump's output pressure.
In a prior art rolling diaphragm pump, the differential pressure across the diaphragm is determined by the pump dimensions and the working pressure. For a given pump size, the differential pressure increases as the working pressure increases. This not only reduces the lifetime of the diaphragms but also limits the maximum pressure of the pump.
A dual-unit pump, e.g., a rolling diaphragm piston pump, is disclosed in U.S. Pat. No. 4,543,044, the entire contents of which are incorporated herein by reference thereto. The pump is suitable for pumping an abrasive high-viscosity slurry, and is adapted to operate at a constant flow rate by means for detecting and correcting a pressure differential in the two units before the units switch from the pumping cycle to the filling cycle and vice versa. The flow of liquids is controlled by valves of the type which switch the flow to and from the units with essentially no volume change in the liquid inlet and outlet lines.
Turning to
In
According to the design of pump 10 in
F
down
=P
1
·A
1
+P
2
·A
4
+P
3·(A3−A4) (Eq. 1)
The upward force is determined by Equation 2 below:
F
up=(P2·A2)+[P4·(A3−A4)] (Eq. 2)
Area A1 is the same as area A2, pressure P2 is the same as pressure P4, and pressure P3 is zero pressure with respect to atmosphere. Thus, the upward force must balance the downward force as in Equation 3 below:
(P1·A1)+(P2·A4)=(P2−A1)+[P2·(A3−A4)] (Eq. 3)
This balance can be simplified as shown in Equations 4-6 below:
Thus, as shown in Equation 6, ΔP is dependent on working pressure.
Pumping high viscosity liquids and slurries at high pressure and/or at constant pressure or constant flow rate is particularly difficult. High viscosities slurries, for example, may be between 10,000 and 5,000,000 centipoise, and may be abrasive and include large particulates such as rocks ⅛ inch in general size. However, pumping pressures in prior art rolling diaphragm pumps are limited by the pressure that the diaphragm can withstand. The differential pressure ΔP varies with discharge pressure P1 and therefore if P1 becomes too high, ΔP can become so high that the diaphragm integrity is lost and the diaphragm breaks.
It is desired that the differential pressure ΔP is in the range of 10 psi to 20 psi so that the diaphragm is maintained in the correct shape and position, while not being overstressed. The prior art rolling diaphragm pump permits this but only for a fixed range of discharge pressure P1 as will be further described herein.
A rolling diaphragm pump may include a housing, a rolling seal diaphragm disposed in the housing, a piston for driving the diaphragm, and a valve for regulating the flow of working fluid in a portion of the housing. A constant differential pressure may be maintained across the diaphragm independent of discharge pressure of the pump. In some embodiments, the rolling seal diaphragm is top hat shaped. Also, the constant differential pressure may be between 1 psi and 100 psi, between 10 psi and 50 psi, or between 10 psi and 20 psi. The discharge pressure may be greater than 1000 psi or greater than 500 psi.
A method of pumping a viscous medium may include: pumping the viscous medium by maintaining a constant differential pressure across a rolling seal diaphragm independent of discharge pressure of the viscous medium, with the diaphragm disposed between the viscous medium and a working medium and being driven by a piston. The viscous medium may be discharged at a constant flow rate or discharged at a constant pressure. The method may further include: regulating the flow of the working medium. In the method, the rolling seal diaphragm may be top hat shaped. Also in the method, the constant differential pressure may be between 1 psi and 100 psi, between 10 psi and 50 psi, or between 10 psi and 20 psi. In the method, the discharge pressure may be greater than 1000 psi or greater than 500 psi. Further, in the method, the viscous medium may be a slurry with a viscosity between 10,000 and 5,000,000 centipoise. Also, the viscous medium may include aggregate with a maximum lateral dimension of ¼ inch or aggregate with a maximum lateral dimension of ⅛ inch.
In one embodiment of the invention, a rolling diaphragm pump creates a positive differential pressure through the use of an adjustable check valve that regulates the flow of a working fluid, such as oil, between the driving cylinder and the bottom of the diaphragm by opening when a threshold pressure is met. This provides control of the differential pressure (ΔP) while being independent of the discharge pressure (P1). Advantageously, an increased pressure range is realized in which the rolling diaphragm pump can operate, and variable control of diaphragm stress is permitted.
In some embodiments, a rolling diaphragm allows continuously variable control of the differential pressure across the diaphragm, which is independent of the discharge pressure.
Preferred features of embodiments are disclosed in the accompanying drawings, wherein:
Turning to
Inventive rolling diaphragm pump 100 includes a piston 112, which for example may be formed of nylon, is disposed within a cylindrical housing 113, and is seated with respect to a rolling seal diaphragm 114 such as a top-hat shaped rubber diaphragm. A working medium 116 such as oil fluid and a discharge medium 118 (the medium that is being pumped) are shown. A standard hydraulic cylinder 119 (such as a single-rodded cylinder) includes a fluid region 120 such as having oil therein, and a rod 122. Portion 121 is in communication with housing 113. Piston 112 is used to maintain the shape of diaphragm 114. Diaphragm 114 is coupled along its circumference to housing 113 at regions 127 along axis 125b which is normal to axis 125a (along which rod 122 for example is axially disposed).
In
Because rod 122 is threadably associated with piston 112, oil flows around the threads and on top of rod 122 so that A4 does not effect A2. Therefore, A1 is the same as A2. The pressure of check valve 126, Pcheck, is fully adjustable to suit a given need, the check valve being designed to open when a threshold differential pressure is met. Thus, a constant pressure can be created across diaphragm 114 regardless of the pumping pressure. In other words, regardless of whether the pumping pressure is 500 psi, 1000 psi, or 10,000 psi, the differential pressure ΔP, calculated as P1−P2, is always the same. In contrast, the prior art pump 10 would not function properly at wide ranges of pressures (e.g., 1,000 psi as compared to 10,000 psi) because the differential pressure ΔP would increase as P1 increases and become so great as to compromise the diaphragm. Pump 100 provides constant flow rate or constant pressure performance. Unlike prior art pump 10, inventive pump 100 advantageously permits pumping of viscous mediums with large aggregates (1) at high pressure and/or (2) at constant pressure or constant flow rate over wide pressure ranges. In addition, inventive pump 100 advantageously may permit longer life of operation in high pressure usage than rotating or progressive-type pumps which suffer from substantial wear when pumping media having large aggregates.
The theory of operation of exemplary inventive pump 100 now will be explained. In pump 100, the downward force is determined by the following Equation 7:
F
down=(P1·A1)+(P2−A3) (Eq. 7)
The upward force is determined by Equation 8 below:
F
up=(P2·A2)+(P4·A3) (Eq. 8)
Area A2 is the same as area A1, and the check valve pressure Pcheck is P4−P2. The upward force must balance the downward force as in Equation 9 below:
(P1·A1)+(P2·A3)=(P2·A1)+(P4·A3) (Eq. 9)
This balance can be simplified as shown in Equations 10-12 below:
Thus, as shown in Equation 12, ΔP is independent of the working pressure.
A theoretical performance comparison, based on the above Equations 1-12, is presented below for an exemplary resin pump assuming the following: diaphragm area A1 of 101.6234 in.2, cylinder area A3 of 8.295768 in.2, rod area A4 of 1.484893 in.2, check pressure of 90 psi, diaphragm diameter 11.75 in., piston diameter 11 in., cylinder diameter 3.25 in., and rod diameter 1.375 in. Table 1 shows the theoretical performance of the prior art rolling diaphragm pump while Table 2 shows the performance according to the inventive design, with P1 being the discharge pressure of the medium that is being pumped, P2 being the pressure of the hydraulic fluid under the piston, and ΔP being P1−P2.
As evident from Table 1, in the prior art design the ΔP is dependent on the working pressure, while in the exemplary inventive design ΔP is independent of the working pressure.
A theoretical performance comparison, based on the above Equations 1-12, also is presented below for an exemplary catalyst pump assuming the following: diaphragm area A1 of 44.17875 in.2, cylinder area A3 of 8.295768 in., rod area A4 of 1.484893 in.2, check pressure of 35 psi, diaphragm diameter 7.75 in., piston diameter 7.25 in., cylinder diameter 3.25 in., and rod diameter 1.375 in. Table 3 shows the theoretical performance of the prior art rolling diaphragm pump while Table 4 shows the performance according to the inventive design, with P1 being the discharge pressure of the medium that is being pumped, P2 being the pressure of the hydraulic fluid under the piston, and ΔP being P1−P2 as in the examples above.
A suitable diaphragm 114 may be a rolling seal diaphragm obtained for example from Bellofram Corporation, of Newell, W. Va. Exemplary diaphragms and methods of use are disclosed in U.S. Pat. Nos. 3,137,215 and 3,373,236, each of which is incorporated herein by reference thereto.
While various descriptions of the present invention are described above, it should be understood that the various features can be used singly or in any combination thereof. Therefore, this invention is not to be limited to only the specifically preferred embodiments depicted herein.
Further, it should be understood that variations and modifications within the spirit and scope of the invention may occur to those skilled in the art to which the invention pertains. Accordingly, all expedient modifications readily attainable by one versed in the art from the disclosure set forth herein that are within the scope and spirit of the present invention are to be included as further embodiments of the present invention. The scope of the present invention is accordingly defined as set forth in the appended claims.
The benefits of U.S. Provisional Application No. 60/886,919 filed Jan. 26, 2007 and entitled “Rolling Diaphragm Pump” are claimed under 35 U.S.C. § 119(e), and the entire contents of this provisional application are expressly incorporated herein by reference thereto.
| Number | Date | Country | |
|---|---|---|---|
| 60886919 | Jan 2007 | US |
