Apparatus and method for jetting a cable into a duct

Abstract

A method for installing an elongated element into a duct by pushing the elongated element into the duct through a pressure chamber, introducing pressurized fluid into the duct at a nominal pressure, and applying a driving force. The method including monitoring fluid pressure into the duct and the driving force and reducing the fluid pressure to a predetermined value lower than the nominal pressure.

Claims

1. A method for installing an elongated element into a duct, comprising the steps of: inserting the elongated element into the duct through a pressure chamber located at an entry of the duct, by applying a driving force (F.sub.a) to the elongated element, resulting in an effective pushing force (F.sub.2eff) downstream the pressure chamber, introducing pressurized fluid into the duct at a nominal pressure, through the pressure chamber, wherein, after an instant when said elongated element has entered the duct and before an instant when said elongated element reaches a final position into the duct, the method comprises the steps of: monitoring at least fluid pressure (p.sub.a) into said duct and said driving force (F.sub.a), reducing said fluid pressure (p.sub.d) to a predetermined value lower than the nominal pressure, in relation to said driving force (F.sub.a), wherein the driving force (F.sub.a) is applied upstream an entry of the elongated element into the pressure chamber so as to push the elongated element into the pressure chamber with an external pushing force (F.sub.2), and wherein the fluid pressure (p.sub.a) is reduced if the fluid pressure (p.sub.d) results in an axial outward pressure force applied to the elongated element susceptible to be equal or greater than the external pushing force (F.sub.2).

2. A method according to claim 1, wherein the external pushing force (F.sub.2) is equal to the driving force (F.sub.a) subtracted with a force to pull the elongated element from a reel (F.sub.1).

3. A method according to, claim 1 wherein fluid pressure (p.sub.d) is reduced if: $\frac{F_{2\mathrm{eff}}}{F_{\mathrm{bc}}}\le 0.1;$ where: $F_{2\mathrm{eff}}=F_a-F_1-F_i;$ $F_i=\frac{\pi }{4}{D}_c^2{p}_d;$ $F_{\mathrm{bc}}=\frac{\pi }{4}{D}_c{D}_d{p}_d;$ F.sub.a: applied and measured driving force; F.sub.1 applied and measured force to pull the elongated element from a reel; F.sub.bc: applied and measured pressure force to the elongated element at the pressure chamber; D.sub.c: elongated element diameter; D.sub.d: Duct internal diameter; p.sub.d: fluid pressure.

4. A method according to, claim 1, comprising a step of: uncoiling the elongated element from a reel before pushing the elongated element into the duct; measuring a pulling force (F.sub.1) applied to the elongated element to uncoil the elongated element; correcting the driving force (F.sub.a) by the measured pulling force (F.sub.1), to obtain the effective pushing force (F.sub.2eff) and to decide if fluid pressure (p.sub.d) shall be reduced.

5. A method according to claim 4, wherein the step of measuring the pulling force comprises a step of measuring a transverse force applied to the elongated element, between the reel and a driving means arranged to apply the driving force (F.sub.a).

6. A method as claimed in claim 5, the driving means comprising a pushing unit, the pushing unit comprising upper and lower mechanically driven belts.

7. An apparatus as claimed in claim 6, the measure and control unit including one or more of a strain gauge, a calibrated spring, a fluid pressure gauge, a thermometer, or an idle wheel or drive wheel.

8. A method according to, claim 1, wherein the fluid is gas and the fluid pressure (p.sub.d) is gas pressure.

9. A method according to claim 8, wherein elongated element velocity (v.sub.c) is monitored, and wherein the gas pressure (p.sub.d) is reduced if the elongated element velocity (v.sub.c) is lower than a predetermined speed, and/or if an undulation/deviation from a taut position of the elongated element in the duct is detected.

10. A method according to claim 8, wherein the step of reducing the gas pressure (p.sub.d) comprises a step of venting the gas pressure (p.sub.d) by opening an orifice at the entry of the duct.

11. A method according to claim 8, wherein the step of reducing the gas pressure (p.sub.d) is followed by a step of increasing the gas pressure (p.sub.d) in relation to said driving force (F.sub.a).

12. A method according to claim 11, wherein if an abrupt increase of the gas pressure (p.sub.d) up to the nominal pressure is applied to the duct, a constant decrease of pressure per meter along said duct is reached at a given time t.sub.c, and wherein the step of increasing the gas pressure (p.sub.d) is done at a rate so that the nominal pressure is reached at a time t.sub.M comprised in the range: 0.15t.sub.c≤t.sub.M≤0.5t.sub.c.

13. A method according to claim 11, wherein the steps of reducing the gas pressure (p.sub.d) and increasing the gas pressure (p.sub.d) are repeated several times before the instant when said elongated element reaches the final position into the duct.

14. A method according to claim 13, wherein if several sequences of pressure decrease and pressure increase are performed, the last sequence is performed so that the pressure increase ends to supply gas at a nominal pressure greater than the nominal pressure achieved by the previous sequences and lower than a nominal pressure creating a pressure force equal or greater than: the external pushing force (F.sub.2) if the driving force (F.sub.a) is applied upstream the entry of the elongated element into the pressure chamber, the driving force (F.sub.a) subtracted with a force to pull the elongated element from a reel (F.sub.1), if the driving force (F.sub.a) is applied downstream of the entry of the elongated element into the pressure chamber.

15. A method for installing an elongated element into a duct, comprising the steps of: inserting the elongated element into the duct through a pressure chamber located at an entry of the duct, by applying a driving force (F.sub.a) to the elongated element, resulting in an effective pushing force (F.sub.2eff) downstream the pressure chamber, introducing pressurized fluid into the duct at a nominal pressure, through the pressure chamber, wherein, after an instant when said elongated element has entered the duct and before an instant when said elongated element reaches a final position into the duct, the method comprises the steps of: monitoring at least fluid pressure (p.sub.d) into said duct and said driving force (F.sub.a) reducing said fluid pressure (p.sub.d) to a predetermined value lower than the nominal pressure, in relation to said driving force (F.sub.a), wherein the driving force (F.sub.a) is applied downstream an entry of the elongated element into the pressure chamber so as to pull the elongated element into the pressure chamber with an effective pulling force (F.sub.1eff), and wherein the fluid pressure (p.sub.d) is reduced if the fluid pressure (p.sub.d) results in an axial outward pressure force (F.sub.i) applied to the elongated element susceptible to be equal or greater than the driving force (F.sub.a) subtracted with a force to pull the elongated element from a reel (F.sub.1).

16. A method according to claim 15, wherein the effective pulling force (F.sub.1eff) is equal to the sum of the pressure force (F.sub.i) and a force to pull the elongated element from the reel (F.sub.1).

17. An apparatus configured to implement the method for installing an elongated element into a duct as claimed in claim 15.

18. An apparatus for installing an elongated element into a duct, comprising: a pressure chamber connected to an entry of the duct, and arranged to be pressurized at a nominal pressure, a driving unit arranged to apply a driving force (F.sub.a) to the elongated element upstream of an entry of the elongated element into the pressure chamber so as to push the elongated element through the pressure chamber and into the duct with an external pushing force (F.sub.2), a monitoring unit, arranged for monitoring at least a fluid pressure (p.sub.d) into the duct and the driving force (F.sub.a), a control unit arranged to automatically reduce the fluid pressure (p.sub.d) in relation to said driving force (F.sub.a), wherein the fluid pressure (p.sub.d) is reduced if the fluid pressure (p.sub.d) results in an axial outward pressure force applied to the elongated element susceptible to be equal or greater than the external pushing force (F.sub.2).

19. An apparatus according to claim 18, further comprising: a reel arranged to supply the elongated element to the driving unit at a predetermined angle, a transverse force measuring unit, arranged between the unreeling unit and the pushing unit, to measure a transverse force and/or an axial force being a pulling force applied to the elongated element to unreel the elongated element.

20. An apparatus according to claim 18, wherein the monitoring unit is arranged for monitoring an elongated element velocity (v.sub.c), and wherein the control unit is arranged to automatically reduce the duct pressure in relation to said elongated element velocity (v.sub.c).

21. An apparatus as claimed in claim 18, the driving unit comprising upper and lower mechanically driven belts.

22. An apparatus as claimed in claim 18, the monitoring unit comprising a measure and control unit for measuring one or more of motor pressure, cable radial force, fluid pressure, fluid temperature, cable position, cable velocity, or belt velocity.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other features and advantages of the present invention will appear more clearly from the following detailed description of particular non-limitative examples of the invention, illustrated by the appended drawings where:

(2) FIG. 1a represents a sketch of an apparatus according to a first embodiment of the invention;

(3) FIG. 1b represents a sketch of an apparatus according to a second embodiment of the invention;

(4) FIG. 2 is a detailed sketch of an apparatus according to the first embodiment of the invention, and arranged to carry out the method of the present invention;

(5) FIG. 3 represents the apparatus of FIG. 2, with an option to measure a transverse force during uncoiling an elongated element;

(6) FIG. 4 represents pressure as a function of x in a duct for different time after opening a valve at 16 bar from zero pressure with a cable of a given external diameter and an the duct having a given internal diameter and a given length;

(7) FIG. 5 represents the gradient of pressure as a function of x for the pressure curves shown on FIG. 4.

DETAILED DESCRIPTION

(8) In the present application, it is referred to elongated elements, which may be for example, cables, electric cables, optical fibers or cables, temperature sensing optic fibers or cables. All these elongated elements may comprise for example a core, a coating, or a sheath. However, the wording elongated element is not limited to any of these specific examples.

(9) It is also referred to ducts, which may be for example pipes, hollow cylinders, tubes, conduits: anything defining a channel in which an elongated element may be laid in or out, from a first location to a second location.

(10) FIG. 1a represents a sketch of an apparatus according to a first embodiment of the invention, to illustrate the forces involved during the laying of an elongated element (cable 2) into a duct 6, performed with a driving unit via a pressure chamber 12, when the driving unit is a pushing unit 8 arranged upstream the entry of the cable 2 into the pressure chamber 12.

(11) The force from the reel is a pulling force, the three from the drive F.sub.a is a traction force, the external pushing force after the mechanical drive F.sub.2 and the insertion force F.sub.i are pushing forces and the force F.sub.2eff is an effective pushing force. The following formulas apply:
F.sub.a=F.sub.1+F.sub.2
F.sub.2eff=F.sub.2−F.sub.i
Then:
F.sub.2eff=F.sub.a−F.sub.1−F.sub.i

(12) Example: Pulling force F.sub.1 from reel 5 N, traction force F.sub.a from mechanical drive 10 N, pushing force after mechanical drive 5 N, insertion (pushing) force F.sub.i 1 N and effective pushing force F.sub.2eff 4 N.

(13) FIG. 1b represents a sketch of an apparatus according to a second embodiment of the invention, to illustrate the forces involved during the laying of an elongated element (cable 2) into a duct 6, performed with a driving unit via a pressure chamber 12, when the driving unit is a pulling unit 8a arranged downstream the entry of the cable 2 into the pressure chamber 12.

(14) The pulling force from the reel F.sub.1, the insertion force F.sub.i and the force F.sub.1eff are pulling forces, the force from the drive F.sub.a is a traction force and the force after the mechanical drive F.sub.2eff is an effective pushing force. The following formulas apply:
F.sub.a=F.sub.1eff+F.sub.2eff
F.sub.1eff=F.sub.1+F.sub.i (note the plus sign for F.sub.i)
Then:
F.sub.2eff=F.sub.a−F.sub.1−F.sub.i

(15) Example: Pulling force F.sub.1 from reel 5 N, insertion (pulling) force F.sub.i 1 N, effective pulling force 6 N, traction force F.sub.a from mechanical drive 10 N and effective pushing force F.sub.2eff 4 N after mechanical drive. So, the final result is the same.

(16) FIG. 2 represents an apparatus arranged to lay an elongated element (a cable 2) into a duct 6, when the driving unit is a pushing unit 8. A cable 2 with diameter D.sub.c is installed from a reel 4 into a duct 6 with internal diameter D.sub.d using a device that simultaneously pushes and blows/floats the cable into the duct (in other words, this method is a jetting/floating method). Pushing is done with an axial force F.sub.a by a pushing unit 8, e.g. consisting of mechanically driven lower and upper belts, the latter belt pressed via block 10 onto the cable 2 with radial (pinch) force F.sub.r.

(17) The driving force F.sub.a is the sum of both the pulling force F.sub.1 to pull the cable 2 from the reel 4 and the external pushing force F.sub.2 to push the cable 2 into a pressure chamber 12 (which might be referred to as a blowing chamber as the fluid is gas in present example) and further into the duct 6. Fluid under pressure P.sub.d from a pump/compressor (not shown) is fed into the pressure chamber 12 via orifice 5, resulting in propelling forces exerted onto the cable 2 in the duct 6. The pressure chamber 12 is mounted on a common base plate 14 shared with the pushing unit 8. A wheel 16, also mounted on the base plate 14, follows the cable 2 to measure the distance x installed and, derived from that, the installation velocity v.sub.c,

(18) The apparatus comprises a measure and control unit 20 connected to the pushing unit 8, the pressure chamber 12, and the idle wheel 16 to measure directly (as a function of time) the following parameters:

(19) a) Motor pressure p.sub.m (pneumatic, hydraulic) or voltage or current (electric). Alternatively the driving force F.sub.a is measured on the pushing unit, using a strain gauge.

(20) b) Cable radial (pinch) force F.sub.r. This can be done by a calibrated spring (e.g., with maximum value of 100 N/cm for maximum settings and less, in steps (e.g. a ring indication on a bar sticking out), e.g. 100, 75, 50 and 25 N/cm. Many cables are specified for a crush resistance (between hard flat plates)>100 N/cm, but some smaller cables are specified <100 N/cm. In the latter case the pinch pressure may also need to be measured to guarantee (and prove) correct installation. Belt drives (usually soft and with cable groove) usually allow much larger pinch forces than the specified hard flat plate specification.

(21) c) Fluid pressure p.sub.d in duct (pressure chamber).

(22) d) Fluid temperature T.sub.d in duct (pressure chamber).

(23) e) Cable position x. This is measured by an idle wheel 16 that is pressed (with low force) on the cable 2.

(24) f) Cable velocity v.sub.c. This comes from the same sensor as for e).

(25) g) Belt velocity v.sub.d. This is measured on the wheels which drive the belt.

(26) FIG. 3 shows the apparatus of FIG. 2, equipped with a transverse force measuring unit 18, arranged between the reel 4 and the pushing unit 8, to measure a transverse force so as to deduct an axial force being a pulling force applied to the cable 2 to unreel the cable 2.

(27) The following parameters are relevant for the installation and are either parameters which are measured directly (see above), or calculated from the latter parameters:

(28) 1) Axial driving force F.sub.a. This is obtained from the system that drives the belts or wheels, by e.g. pneumatic, hydraulic or electric motors, see a). Either the force of the drive system is measured directly (e.g. by a strain gauge) or derived from the torque of the motor. Often the torque of the motor depends on the speed of the motor. Therefore the axial force on the cable is corrected for the speed of the motor (belt), which is measured in g).

(29) 2) Cable radial (pinch) force F.sub.r. This is directly measured by b).

(30) 3) Fluid pressure p.sub.d in duct (pressure chamber). This is directly measured by c).

(31) 4) Fluid temperature T.sub.d in duct (pressure chamber). This is directly measured by d).

(32) 5) Cable position x. This is directly measured by e).

(33) 6) Cable speed v.sub.c. This is directly measured by f).

(34) 7) Slip: This uses the cable speed v.sub.c, measured by f), and the belt velocity v.sub.d, measured by g). The slip follows from the difference in both speeds.

(35) From the above measured parameters, it is possible to calculate and predict when a critical situation can appear, leading to damage of the cable 2, or to a stop in the floating/jetting process. In particular, it is advantageous to make sure that the pushing unit applying a driving force F.sub.a, resulting in a external pushing three F.sub.2, and the pressure chamber 12 pressurized at p.sub.d are set to create an effective floating/jetting (for the latter effective synergy between pushing and blowing). In this aim, the Applicant found particularly advantageous to calculate the parameter C.sub.j as:

(36) $\frac{F_{2\mathrm{eff}}}{F_{\mathrm{bc}}}\equiv C_j,$
where:

(37) $F_{2\mathrm{eff}}=F_2-F_i;\mathrm{or}{F}_{2\mathrm{eff}}=F_a-F_1-F_i$$F_i=\frac{\pi }{4}{D}_c^2{p}_d;$$F_{\mathrm{bc}}=\frac{\pi }{4}{D}_c{D}_d{p}_d;$ F.sub.2: external pushing force; F.sub.a: applied and measured driving force; F.sub.1: applied and measured force to pull the elongated element from reel; D.sub.c: elongated element diameter D.sub.d: Duct internal diameter; p.sub.d: gas pressure.

(38) The Applicant found advantageous to have during the installing operation C.sub.j always greater than 0, and for jetting even greater than 0.2 and more preferably 0.1. Indeed, when C.sub.j<0 the installing performance can be very bad. In the latter case the cable 2 will be under tensile load once inserted in the duct and the capstan effect is present from the start, killing the fluid drag trick of avoiding the capstan effect. In the case of jetting the effective pushing forces F.sub.2eff (after insertion in the duct) shall be also at least a fraction of the cumulative blowing forces, to create the synergy between pushing and blowing. When the external pushing force F.sub.2 (and driving force F.sub.a) is limited, the duct air pressure p.sub.d might be too large, and needs to be decreased for optimum performance with (C.sub.j>0.1. In other words, when the factor C.sub.j becomes less than 0.1 the duct air pressure shall be decreased until the C.sub.j value of 0.1 is reached again, for optimal jetting. Jetting can then be performed as long as this condition is met (C.sub.j equal or above 0.1).

(39) When the elongated element slows down or stops (if the velocity v.sub.c is measured below a minimum value, i.e. cable speed is zero or almost zero), the invention proposes to significantly decrease the gas pressure with complete venting of the duct and to increase again the gas pressure (as long as C.sub.j value allows this increase), to benefit from a specific and temporary state of gas flow in the duct 6, and to achieve again a movement of the elongated element.

(40) Indeed, as gas is a compressible medium, the pressure along the duct is not linear, and as shown FIG. 4, a sudden or abrupt increase of pressure in a duct, starting from a completely vented duct will create an evolution of the pressure profile along this duct. As visible FIG. 4, 1 minute after pressurization, the pressure decrease from 16 bars to atmospheric pressure from entry to approx. 1300 meters from entry. At 4 minutes, almost all the duct is pressurized, and after 10 minutes, the flow is established, with a small linear pressure decrease from entry to 1500 meters from entry, and a more and more important decrease as far the position is close to the exit.

(41) The important curve to note is after 6 minutes, where the decrease of pressure looks like a linear decreasing function all along the total length of the duct. This means that at this specific time after start of pressurization, the drag force along the cable 2 will be quite uniform. This specific and temporary state of flow creates good conditions to jet or restart to jet the cable 2 a bit further in the duct 6.

(42) FIG. 5 shows the loss of pressure per meter all along the duct, at the same timings as the ones of FIG. 4. After 1 minute from pressurization, the gradient of pressure is very important at the entry of the duct (out of scale), and 10 minutes after pressurization, the gradient of pressure close to the exit is more than double than the one at the entry. Only after 6 minutes, the gradient of pressure varies less than ±30% of its average value, which is considered to be quite stable and constant. The specific state of flow at 6 minutes after pressurization creates a drag force along the entire length of the cable 2 which is quite uniform and this helps to move further the cable 2, or to recover a movement of the cable 2 after a stop. This time to get this specific and temporary “constant decrease of pressure” along the duct's length is called t.sub.c, and depends from several parameters, and for example the duct internal diameter, the cable external diameter, the duct's length, the nominal pressure, the gas temperature. . . . The time t.sub.c is specific to each configuration, and can be calculated by means of simulation.

(43) FIGS. 4 and 5 shows as well that an abrupt pressurization creates, immediately after opening of the valve, drag forces onto the portion of cable 2 located close to the pressure chamber (at 1 minute after pressurization, there is no pressure between 1500 and 2500 meters). Consequently, a great flow of compressed air is present only close to the entry of the duct, and if the pressurization is done while the cable 2 is almost laid, its portion close to the entry will be subjected to high flow, despite its portion at the end of the duct is not subjected to any drag/propelling force (as the air flow is still not established there). There might be a risk of tangling, if the cable 2 presents loose portion close to the entry (which is typically the case if jetting has been stopped because deviation or undulations have been detected), as all the loose portions will be pushed, ending in some cases in a tangle. This situation is likely to happen when a bundle of fibers are laid together, and one fiber of these fibers is stopped (blocked against a duct's connector for example).

(44) The Applicant found very advantageous to avoid such abrupt and sudden increase of pressure while increasing again the pressure in the pressure chamber. In particular, when an abrupt increase of gas pressure up to the nominal pressure is applied to the unpressurized duct, the constant decrease of pressure per meter along the duct is reached at the given time t.sub.c, and the increase of gas pressure to apply to minimize the risks of tangling should be done at a rate so that the nominal pressure is reached at a time t.sub.M comprised in the range: 0.15t.sub.c≤t.sub.M≤0.5t.sub.c. In other words, it is found to set the pressure ramp up so that nominal pressure is recovered between 6 and 2 times faster than time t.sub.c.

(45) It is of course understood that obvious improvements and/or modifications for one skilled in the art may be implemented, still being under the scope of the invention as it is defined by the appended claims. In particular, it is referred to the laying of a cable, but the method is well suited to lay fibers, optical fibers, and especially fibers with low stiffness, as they present a high risk of damage if bended or pushed into the pressure chamber while undulations, buckling or a stop occur into the duct.