US 2253152 A
Description (OCR text may contain errors)
Patented Aug. 19, 1941 UNITED STATES PATENT OFFICE 2,253,152 HIGH SPEED RECIPROCATING RAM PUMP Frank Hathorn Towler and John Maurice Towler,
Yorkshire, England Application August 1, i938, Serial No. 222,518 In Great Britain August 16, 1937 1 Claim.
to dispense with the necessity of a by-pass and a relief valve but in such a way that the pump continues to run but ceases to discharge liquid from the pump chamber when'the predetermined maximum pressure above the discharge valve is attained but if the pressure falls due to leakage the pump automatically makes up the leakage so that in the case for instance of, its application to a hydraulic baling press, positive stops may safely be used at the limit of movement of the press rams, and the pump will maintain the bale under pressure until it has been securely wired.
ner that the displacement member continues to displace the imprisoned liquid without causing any of said imprisoned liquid to be discharged.
The attainment of a similar object has been attempted by placing a vessel full of liquid in permanent communication with the cylinder or chamber of an ordinary hydraulic pump the cat pacity thus produced being predetermined so that the displacement of the pump piston or ram does not produce more than a certain predetermined pressure within the pump cylinder.
In this prior proposal the connection between the vessel and the pump chamber consisted of a comparatively long and small bore pipe having a right-angled bend in. its length.
From experiments we have made with reciproeating ram pumps having such a permanently connected vessel we have proved that the arrangement heretofore proposed is impracticable for a pump which is required to deliver a substantial quantity of liquid at low pressure. We have found that air, which is normally held in solu-- tion in the liquid, is liberated in the pump chamber when the pressure is released. The air so liberated finds its way into the horizontal portion of the restricted passage connecting the pump chamber to the said permanently connected vessel. Then as the pressure against which the pump has to deliver increases, the liquid in the pump chamber is compressed on the delivery stroke and passes along thehorizontal passage around the bend and so into the said vessel, carrying the air with it. As the pressure increases still further, this air is forced into solution with the liquid in the said permanently connected vessel, so that the resilience of the liquid in the vessel is not seriousl affected and the pump functions quite satisfactorily at maximum pressure. However, as soonas the pressure against which the pump has to deliver is released, for more than a momentary period, the air in the permanently connected vessel comes out of solution and being trapped by the bend in the restricted connectingpassage it accumulates and forms an air cushion between the vessel and the pump chamber. This air cushion seriously reduces the volumetric efficiency of the pump at low pressures and, as the air continues to accumulate in the passage, the pump becomes very nearly ineffective at low pressures. On the other hand, if the delivery passage of the pump is completely closed, the pump is usually sufliciently effective to build sufficient pressure in the said permanently connected vessel to cause the air to go into solution again so that the pump again functions satisfactorily at maximum pressure. Thus, a pump, particularly a pump running at high speed, constructed as heretofore will function satisfactorily at maximum pressure, when the delivery of the pump is zero, or at pressures approaching the maximum when the delivery of the pump is comparatively insignificant, but the pump is practically ineffective at low pressures.
W have found that for complete success the following conditions must be fulfilled:
(1) The pump must operate at relatively high speeds and pressures so as to keep the size of the connected vessel reasonably small.
(2) The ram should, for preference, practically fill the pump chamber on the-discharge strok so as almost completely to expel air or other gas liberated from the liquid during umpin (3) The connected vessel or chamber must be so situated in relation to the pump discharge valve that any air in the vessel or chamber passes automatically and freely to the discharge ilalve to be expelled by the pump. The air mayfpass to the discharge valve in any one of" the following manners:
The use of an additional capacity in communi-- cation with the pump chamber of a reciprocating ram pump for the purpose of controlling the pumps delivery is really impracticable in the case of slow speed pumps (60 to 150 R. P. M.) as owing to the very large displacement of such pumps the additional capacity required would have to be relatively enormous. For example in the case of a high speed pump running at 1500 R. P. M. the 'ram displacement would be one tenth of that of an equivalent pump of the same power which ran at 150 R. P. M. In consequence the high speed pump would require an additional capacity one tenth that required by the slow speed pump assuming the pressure to be the same in each case. Of course if the slow speed pump operates at a lower pressure the size of the capacity will have to be correspondingly greater.
While it is preferred that the pump ram shall almost completely fill the pump chamber on the discharge stroke this is not an absolute necessity for success and for this reason it is not intended that the invention shall be limited in this'respect but for best results it is advisable that the condition shall obtain.
The present invention may, therefore, be said to consist broadly of a positive displacement pump of the high speed, high pressure type having a vessel or chamber of predetermined capacity in communication with the pump chamber of the pump so as to increase the effective capacity of said pump and in such relation to the pump discharge valve that any air in the vessel or chamber passes freely and. automatically and in a substantially direct line to the discharge valve the capacity of said vessel or chamber being such that liquid will automatically be imprisoned in the pump chamber capacity at a predetermined maximum pressure above the discharge valve and the displacement member or ram will, at such maximum pressure, continue to displace the imprisoned liquid without causing any of said imprisoned liquid to be discharged.
In order that the invention may be clearly understood and carried into effect an embodiment showing the use of a closed vessel and another embodiment showing the use of a vessel through which the pump discharges will now be described by aid of the accompanying, somewhat diagrammatic drawing in which:
Fig, l is a vertical longitudinal section through a high speed reciprocating ram pump having a closed vertically disposed vessel.
Fig. 2 is a similar view but illustrating the embodiment in which the discharge valve is on the the kind described in the specification of our co-- pending application No. 146,038 in which the pump ram almost completely fills the pump bore at the inner end of each stroke so as almost completely to empty the pump bore of liquid before each suction stroke.
In the drawing a indicates the pump body, b the pump ram, 0 the pump chamber, d a mushroom type inlet valve situated at the inner end of the pump chamber so as to oppos the end of the ram, e the discharge valve, 1 the large capacity chamber or vessel, 9 a straight and nonrestricted passage forming a communication between the interior of the vessel 1 and the pump chamber h a ball or roller bearing mounted directly upon an eccentric i for imparting the inward or discharge stroke to the ram and 1 pockets for th reception of springs for returning the ram on each suction stroke.
As shown the vessel j is vertical and below the pump chamber so that any air released passes automatically and freely to the'discharge valve to be expelled by the pump. In the, example illustrated in Figure 2 the vessel 1 may be above the pump chamber as any air released will be carried out of the pump at each discharge as will hereafter appear.
The example illustrated in Fig. 2 differs from the example illustrated in Fig, l in that the vessel I has an opening at its upper end which is controlled by the discharge valve of the pump.
By this means the liquid within the vessel is kept constantly changed as the interior of the vessel constitutes a section of the discharge passage through which the pump delivers during each discharge stroke. The collection 01' air within the vessel or the. restricted passage g is thus rendered impossible or at least negligible.
One of the principal uses of a pump according to the present invention is in connection with a hydraulic baling or bundling press and to further explain the uses and operation of a pump according to the present invention particulars of such an application will now be given in the following description.
In this application of the invention the hydraulic press is of normal construction excepting that the control valve has no mid-position, as when the bale is fully compressed the pump still continues to deliver liquid to the press cylinders, positive stops being provided to prevent the bale being compressed any further.
With a conventional pump the delivery of the pump would in this case have to be by-passed or allowed to escape through a relief valve or the pump would have to be stopped.
In the present invention the pump is of the reciprocating ram type having one or more rams and each pump chamber is made of very large capacity in relation to the pump ram displacement by the use of the aforesaid additional capacity vessel 1. Consequently, as the pressure in the press cylinders increases the pump ram has first to compress the liquid in the pump chamber before lifting the pump delivery valve and delivering the liquid to the press cylinder; and the amount of liquid delivered at each stroke of the pump ram is reduced by the amount which the liquid has to be compressed in order to overcome the pressure in the press cylinders and lift the delivery valve. The capacity of the-pump chamber is so arranged in relation to the pump ram displacement that, when a predetermined maximum pressure is reached, the full inward stroke of the pump ram is only sufficient to compress the liquid to the. requisite pressure, but it is not sufllcient to lift the pump delivery valve against the pressure already attained in the press cylinders. That is to say that, as the pump ram continues to reciprocate, the liquid in the pump chamber compresses and expands in unison; so that, with the exception of the frictional. losses, the energy expended in compressing the liquid in the pump chamber is given back to the pump shaft on the return stroke when the liquid is allowed to expand. Thus, when the bale is fully compressed and the press table is prevented from compressing it any further because of the stops so provided, the predetermined maximum pressure is reached and the pump continues to run at full speed but without delivering any liquid into the cylinders, so that the power required to'drive the pump at maximum pressure is only that .necessary to overcome frictional losses; and,
since there is no delivery of liquid by the pump, there is no need to provide a relief valve or other form of by-pass. It will be understood, further, that, as the pressure increases up to the maximum, the delivery of the pump decreases proportionately, so that over a wide range of pressure variation the lower required to drive the pump remains substantially constant. Thus, for sake of explanation we will take a specific example. Let us imagine a single ram pump having a ram displacement each stroke of 0.35 cubic inch and we will assume that the liquid compresses 3 cubic inches per 1,000cubic inches volume per 1,000 lbs. per sq. inch increase in pressure. If we make the pump chamber of 16.67 cubicinches capacity, then the liquid in the chamber will compress 0.05 cubic inch per'1,000 lbs. per sq; inch increase in pressure. Therefore, if we drive the pump at 1.000 R. P. M. it will deliver 350 cubic inches per minute atno pressure at a theoretical pump 1 horse-power of zero; 'and at 7,000 lbs. per sq. inch the liquid in the chamber will compress 0.35 cubic inch at each stroke of the ram, so that the open the communication between the pump chamber and the capacity chamber such valve being operated automatically. Further the capacity of the permanently connected vessel may be made variable by suitable means such as by disposing within the same a longitudinally adjustable piston so as to vary the maximum pressure at which the pump will give zero delivery.
In a reciprocating ram pump, in combination, a pump body, a bore in said body, a ram slidable within said bore, means for reciprocating said ram, a pump chamber. at the inner end of said bore, a supplementary chamber extending outwards from said pump body at right angles to said bore, a straight unrestricted passage 'at the inner end of the supplementary chamber and connecting the interior of said supplementary chamber with the pump chamber, and a valve controlled discharge opening in line with and at the outer end of the supplementary chamber and opposing said straight unrestricted passage whereby the liquid being pumped is caused to pass through said supplementary chamber, the arrangement being such that the supplementary chamber provides, with the pump chamber, a
capacity for retaining a body of liquid of such theoretical pump horse-power will again be zero;
but between 2,000 lbs. per sq. inch and 5,000 lbs. per sq. inch the theoretical pump horse-power varies from 1.25 horse-power to 1.5 horse-power and back again to 1.25 horse-power at 5,000 lbs. per sq. inch and the pump delivery varies from 250 cubic inches per minute at 2,000 lbs.per sq. inch to 100 cubic inches per minute at 5,000- lbs.
per sq. inch. The above figures are approximate and no allowance has been made for friction or loss of volumetric eiiiciency in the pump. It will be understood that this invention may be applied to a high speed reciprocatlng ram pump such as predetermined volume that the same is compressible by the ram to'cause the delivery of the a pump to decrease proportionately to increase of a pressure above the discharge valve "until a predetermined maximum pressureis reached, whilst free air within said body of liquid passes freely and in a substantially direct line outwards through the supplementary chamber to the discharge. valve for removal with the liquid being pumped.
FRANK HATHORN TOWLER.
JOHN MAURICE TQWLER.