ROLLING DIAPHRAGM PUMP

Info

Publication number: 20080260551
Type: Application
Filed: Jan 26, 2008
Publication Date: Oct 23, 2008
Inventor: Walter Neal Simmons (Durham, NC)
Application Number: 12/020,539

Abstract

A rolling diaphragm pump includes 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 is maintained across the diaphragm independent of discharge pressure of the pump. A method of pumping a viscous medium includes 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.

Description

Description

CROSS-REFERENCE TO RELATED APPLICATION

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.

FIELD OF THE INVENTION

The invention relates to a pump and product delivery. More particularly, the invention relates to rolling diaphragm type pumps.

BACKGROUND OF THE INVENTION

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 FIG. 1, a rolling diaphragm pump 10 of the prior art is shown. Piston 12, which for example may be formed of nylon, is disposed within a cylindrical housing 13 and seated with respect to top-hat shaped rubber diaphragm 14. A working fluid 16 such as oil and a discharge fluid 18 (the fluid that is being pumped) are shown. A standard hydraulic cylinder 19 (such as a double-rodded cylinder with a vented top) includes a fluid region 20 such as having oil therein, rods 22a and 22b, and a vented region 24. Piston 12 is used to maintain the shape of diaphragm 14. Diaphragm 14 is coupled along its circumference to housing 13 at regions 27 along axis 25b which is normal to axis 25a (along which rods 22a, 22b for example are axially disposed).

In FIG. 1, P₁is the discharge pressure of the medium that is being pumped (e.g., to a packaging machine so that the medium may be used to fill a chub), P₂is the pressure of the hydraulic fluid under piston 12 (e.g., the working fluid pressure), P₃is vented to atmosphere and assumed as zero pressure with respect to atmosphere, and P₄is connected to P₂and thus is the same as the pressure of the hydraulic pressure P₂. In addition, for the purposes of this analysis, A₁is the effective area that pressure P₁acts upon to produce force in a direction parallel to axis 25a, A₂is the effective area that pressure P₂acts upon to produce force in a direction parallel to axis 25a, and A₃is the internal area of the hydraulic cylinder 19 about a plane normal to axis 25a. Product is discharged from pump 10 in direction E. Preferably, P₁>P₂in FIG. 1.

According to the design of pump 10 in FIG. 1, the downward force is determined by the following Equation 1 below:

F_down=P₁·A₁+P₂·A₄+P₃·(A₃−A₄) (Eq. 1)

The upward force is determined by Equation 2 below:

F_up=(P₂·A₂)+[P₄·(A₃−A₄)] (Eq. 2)

Area A₁is the same as area A₂, pressure P₂is the same as pressure P₄, and pressure P₃is 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:

$\begin{matrix} [A_{1} \cdot (P_{1} - P_{2})] = [P_{2} \cdot (A_{3} - A_{4})] - (P_{2} \cdot A_{4}) & (Eq . 4) \\ [A_{1} \cdot (P_{1} - P_{2})] = P_{2} \cdot [A_{3} - (2 \cdot A_{4})] & (Eq . 5) \\ Δ P = P_{1} - P_{2} = \frac{(A_{3} - 2 \cdot A_{4})}{A_{1}} & (Eq . 6) \end{matrix}$

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 P₁and therefore if P₁becomes 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 P₁as will be further described herein.

SUMMARY OF THE INVENTION

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.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred features of embodiments are disclosed in the accompanying drawings, wherein:

FIG. 1 shows a prior art rolling diaphragm pump; and

FIG. 2 shows an exemplary embodiment of an inventive rolling diaphragm pump.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning to FIG. 2, an exemplary embodiment of an inventive rolling diaphragm pump 100 is shown. Pump 100 is suitable, for example, for use in pumping mine roof bolt anchoring compositions, water-bearing explosives, food products, concrete, fraccing fluids for oil and gas wells, coal/water slurries, nuclear waste slurries, asphalt, paint, and filled epoxy resins. However, this list is non-exhaustive and a variety of high viscosity liquids and slurries are amendable to pumping in accordance with the exemplary embodiment.

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 FIG. 2, Pt is the discharge pressure of the medium that is being pumped (e.g., to a packaging machine so that the medium may be used to fill a chub), P₂is the pressure of the hydraulic fluid under piston 112 (e.g., the working fluid pressure), and P₄is connected to P₂and is the pressure in fluid region 120 and is greater than P₂by the setting of check valve 126. In addition, for the purposes of this analysis, A₁is the effective area that pressure P₁acts upon to produce force in a direction parallel to axis 125a, A₂is the effective area that pressure P₂acts upon to produce force in a direction parallel to axis 125a, and A₃is the internal area of the hydraulic cylinder 119 about a plane normal to axis 125a. Product is discharged from pump 100 in direction E. Preferably, P₁>P₂in FIG. 2, so that diaphragm 114 does not invert (resulting in accelerated wear of the diaphragm). Moreover, P₄>P₂.

Because rod 122 is threadably associated with piston 112, oil flows around the threads and on top of rod 122 so that A₄does not effect A₂. Therefore, A₁is the same as A₂. The pressure of check valve 126, P_check, 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 A₂is the same as area A₁, and the check valve pressure P_checkis 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:

$\begin{matrix} [A_{1} \cdot (P_{1} - P_{2})] = (P_{4} \cdot A_{3}) - (P_{2} \cdot A_{3}) & (Eq . 10) \\ [A_{1} \cdot (P_{1} - P_{2})] = A_{3} \cdot (P_{4} - P_{2}) & (Eq . 11) \\ Δ P = P_{1} - P_{2} = (P_{4} - P_{2}) \cdot (\frac{A_{3}}{A_{1}}) = P_{check} \cdot (\frac{A_{3}}{A_{1}}) & (Eq . 12) \end{matrix}$

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 A₁of 101.6234 in.², cylinder area A₃of 8.295768 in.², rod area A₄of 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 P₁being the discharge pressure of the medium that is being pumped, P₂being the pressure of the hydraulic fluid under the piston, and ΔP being P₁−P₂.

TABLE 1 P₁(psi) P₂(psi) ΔP (psi) 100 95.02009 4.979909 200 190.0402 9.959817 300 285.0603 14.93973 400 380.0804 19.91963 500 475.1005 24.89954 600 570.1205 29.87945 700 665.1406 34.85936 800 760.1607 39.83927 900 855.1808 44.81918 1000 950.2009 49.79909 1100 1045.221 54.77899 1200 1140.241 59.75890 1300 1235.261 64.73881 1400 1330.281 69.71872 1500 1425.301 74.69863 1600 1520.321 79.67854 1700 1615.342 84.65845 1800 1710.362 89.63836 1900 1805.382 94.61826 2000 1900.402 99.59817

TABLE 2 P₁(psi) P₂(psi) ΔP (psi) 100 92 8.0 200 192 8.0 300 292 8.0 400 392 8.0 500 492 8.0 600 592 8.0 700 692 8.0 800 792 8.0 900 892 8.0 1000 992 8.0 1100 1092 8.0 1200 1192 8.0 1300 1292 8.0 1400 1392 8.0 1500 1492 8.0 1600 1592 8.0 1700 1692 8.0 1800 1792 8.0 1900 1892 8.0 2000 1992 8.0

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 A₁of 44.17875 in.², cylinder area A₃of 8.295768 in., rod area A₄of 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 P₁being the discharge pressure of the medium that is being pumped, P₂being the pressure of the hydraulic fluid under the piston, and ΔP being P₁−P₂as in the examples above.

TABLE 3 P₁(psi) P₂(psi) ΔP (psi) 100 89.24147 10.75853 200 178.4829 21.51706 300 267.7244 32.27559 400 356.9659 43.03412 500 446.2074 53.79265 600 535.4488 64.55118 700 624.6903 75.30971 800 713.9318 86.06824 900 803.1732 96.82677 1000 892.4147 107.5853 1100 981.6562 118.3438 1200 1070.898 129.1024 1300 1160.139 139.8609 1400 1249.381 150.6194 1500 1338.622 161.3779 1600 1427.864 172.1365 1700 1517.105 182.895 1800 1606.346 193.6535 1900 1695.588 204.4121 2000 1784.829 215.1706

TABLE 4 P₁(psi) P₂(psi) ΔP (psi) 100 91.90837 8.091632 200 191.9084 8.091632 300 291.9084 8.091632 400 391.9084 8.091632 500 491.9084 8.091632 600 591.9084 8.091632 700 691.9084 8.091632 800 791.9084 8.091632 900 891.9084 8.091632 1000 991.9084 8.091632 1100 1091.908 8.091632 1200 1191.908 8.091632 1300 1291.908 8.091632 1400 1391.908 8.091632 1500 1491.908 8.091632 1600 1591.908 8.091632 1700 1691.908 8.091632 1800 1791.908 8.091632 1900 1891.908 8.091632 2000 1991.908 8.091632

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.

Claims

1. A rolling diaphragm pump comprising:

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;

wherein a constant differential pressure is maintained across the diaphragm independent of discharge pressure of the pump.

2. The pump of claim 1, wherein the rolling seal diaphragm is top hat shaped.

3. The pump of claim 1, wherein the constant differential pressure is between 1 psi and 100 psi.

4. The pump of claim 1, wherein the constant differential pressure is between 10 psi and 50 psi.

5. The pump of claim 1, wherein the constant differential pressure is between 10 psi and 20 psi.

6. The pump of claim 1, wherein the discharge pressure is greater than 1000 psi.

7. The pump of claim 1, wherein the discharge pressure is greater than 500 psi.

8. A method of pumping a viscous medium comprising:

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.

9. The method of claim 8, wherein the viscous medium is discharged at a constant flow rate.

10. The method of claim 8, wherein the viscous medium is discharged at a constant pressure.

11. The method of claim 8, further comprising:

regulating the flow of the working medium.

12. The method of claim 8, wherein the rolling seal diaphragm is top hat shaped.

13. The method of claim 8, wherein the constant differential pressure is between 1 psi and 100 psi.

14. The method of claim 8, wherein the constant differential pressure is between 10 psi and 50 psi.

15. The method of claim 8, wherein the constant differential pressure is between 10 psi and 20 psi.

16. The method of claim 8, wherein the discharge pressure is greater than 1000 psi.

17. The method of claim 8, wherein the discharge pressure is greater than 500 psi.

18. The method of claim 8, wherein the viscous medium comprises a slurry with a viscosity between 10,000 and 5,000,000 centipoise.

19. The method of claim 8, wherein the viscous medium comprises aggregate with a maximum lateral dimension of ¼ inch.

20. The method of claim 8, wherein the viscous medium comprises aggregate with a maximum lateral dimension of ⅛ inch.